The Decomposition of Ozone-Nitrogen Pentoxide Mixtures Citation Nordberg, Martin Emery (1928) The Decomposition of Ozone-Nitrogen Pentoxide Mixtures. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/JATY-HG31. https://resolver.caltech.edu/CaltechETD:etd-02252005-153549 Abstract No abstract. Item Type: Thesis (Dissertation (Ph.D.)) Subject Keywords: Chemistry Degree Grantor: California Institute of Technology Division: Chemistry and Chemical Engineering Major Option: Chemistry Thesis Availability: Public (worldwide access) Research Advisor(s): Tolman, Richard Chace Thesis Committee: Unknown, Unknown Defense Date: 1 January 1928 Record Number: CaltechETD:etd-02252005-153549 Persistent URL: https://resolver.caltech.edu/CaltechETD:etd-02252005-153549 DOI: 10.7907/JATY-HG31 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 763 Collection: CaltechTHESIS Deposited By: Imported from ETD-db Deposited On: 01 Mar 2005 Last Modified: 03 Oct 2019 23:02 Thesis Files Preview PDF (Nordberg_me_1928.pdf) - Final Version See Usage Policy. 2MB Repository Staff Only: item control page

THE DECOMPOSITION OF OZONE-NITROGEN PENTOXIDE MIXTURES Thesis by Martin Emery Nordberg In partial fulfillment of the requirements for the degree of Doctor of Philosophy _ California Institute of Technology Pasadena, California 1928 TABLE OF CONTENTS 1. Introduction - - - - - - - - 2. The Materials - - - - - - - = 3. Apparatus and Method of Procedure - - - - 4, Computation of the Partial Pressures - - - 5. Experimental Results - - - - - - - a. Ozone Blanks - - - - - - b. The Experiments at Atmospheric Pressure - C.. The Experiments at Reduced Pressure - - 6. The Nitrogen Pentoxide Decomposition - - - 7- The Ozone Decomposition a. b. d. &. Discussion of the Results - 9. Summary General Features of the Reaction - - The Method of Determining the Dependence of the Rate of the Secondary Reaction on Ozone and Nitrogen Pentoxide - - - - The Order of the Secondary Reaction with Respect to Ozone - - - - - The Order with Respect to Nitrogen Pentoxide The Effect of Oxygen - - - - - 10. References - - - - ~- - - - Page 10 10 11 27 31 35 y ~™ YBRE INTRO DUCTION When a mixture of ozone and nitrogen pentoxide is allowed to decompose, the reaction takes place in two stages. During the first stage, while ozone still remains, the ozone immediately oxidizes any nitrogen dioxide formed by the decomposition of nitrogen pentoxide; and the overall result is merely the decomposition of ozone in accor dance with the reactions | Os = W2 02. (1) The second stage of the reaction, after the ozone is all used up, is then the well known first order decomposition of the nitrogen pentoxide! according to the reaction NoOs —> NoOy + 40p = 2N0 + 400. (2) The start of this latter reaction is indicated by a break in the decom- position curve, the slope of the total pressure-time curve being greater at the beginning of the nitrogen pentoxide decomposition than at the end of the ozone decomposition; and also by the formation of brown NOg, which can be readily observed in case the initial pressure of the nitrogen pentoxide is high, 15 mm or mre. The purpose of this research was to study the ozone decomposition, especially the decomposition in the neigh- borhood of the point of inflection of the total reaction curve and pos- sibly get a further insight into the mechanism of the No0s5 decomposition. There is a disagreement among previous investigators concern ing this decomposition. Daniels, Wulf, and Karrer@ in connection with their research on a method of titrating nitrogen tetroxide with ozone, recorded a lag in the time necessary for the appearance of nitrogen . dioxide, which marks the start of the nitrogen pentoxide decomposition. 2 Hirst, 2 in an attempt to duplicate these results, found no similar effect. In two experiments carried out at 20°C and 47°C, he found that the rate of ozone decomposition depended only on the pressure of the nitrogen pentoxide present, as would be the case if the following mechanism were true, | Np0s —> 2N0o + 402 (slow reaction) 2N0p + 03 —> No0s + Op (fast reaction), ‘) Hence the time necessary for the disappearance of the ozone as marked | by the appearance of the brown nitrogen dioxide is given by Pos —_2— 4 + wy) where K, is the specific reaction constant for nitrogen pentoxide, % = PNLOs the partial pressure of the nitrogen pentoxide, and Po, the partial pressure of the ozone. White and Tolman” found, on the other hand, that the time of disappearance of the ozone was considerably less than that calculated by (4) above, quite contrary to the leg first recorded and to the re- sults found by Hirst. They employed a colorimetric method for follow- ing the rate of decomposition of the nitrogen pentoxide, or rather the rate of formation of nitrogen dioxide. The initial pressure of the ozone was determined by trapping a sample of the oxygen-ozone mixture before it passed over the nitrogen pentoxide crystals, measuring its pressure, heating to 150° for 3 hours to decompose the ozone, and again measuring the pressure. Their method did not allow them to follow the actual rate of the ozone decomposition but only to observe the total time necessary for its decomposition. _In the present research it was possible to follow the ozone decomposition as well as that of. the nitre- gen pentoxide. THE MATERIALS The nitrogen tetroxide was prepared by heating C.P. lead nitrate crystals. The water evolved was stopped in a small trap in the line, and the nitrogen tetroxide was then passed thru a phospho- rus pentoxide drying tube and condensed in a tube immersed in an ice-salt mixture. This tube was then sealed off from the generating apparatus, and in the first 20 runs was then connected directly to the apparatus used in determining the rate of decomposition. In the later runs the nitrogen tetroxide was distilled under reduced pressure into a reservoir permanently sealed to the rate apparatus and contain- ing phosphorus pentoxide. The ozone was prepared from Linde tank oxygen dried by passing over phosphorus pentoxide, using a Siemens ozonizer. APPARATUS AND METHOD OF PROCEDURE The preparation of the nitrogen pentoxide and the analysis of the oxygen-ozone mixture were made aw described by White and Tolman. 4 4n oxygen-ozone mixture containing from 3% to 6% of ozone was passed thru jet D,at the rate of from 100 to 150 cc. a minute, where it was allowed to react with nitrogen tetroxide coming from the reservoir C. ' The flow of nitrogen tetroxide was regulated by means of heater G so that it was just decolorized on reaching trap B. After sweeping out the apparatus for several minutes an ice-salt freezing mixture was placed around trap B to condense the solid nitrogen pentoxide. When 4. from 1 to 2 cc. of nitrogen pentoxide had been collected in B, which | took from 1/2 to 2 hours, the nitrogen tetroxide source was shut off - by sealing at constriction H. The pentoxide crystals were further purified by a continued sweeping with the oxygen-ozone mixture for a time varying from 10 minutes to over an hour. The freezing mixture around B was then replaced by a water-bath at temperatures varying from 0° to 30°C, depending on the partial pressure of the nitrogen pentoxide desired in the reaction vessel. The exit gases were run into a wash bottle containing tur- pentine to absorb the ozone and nitrogen pentoxide, and then thru a water aspirator. In the later runs the turpentine was abandoned because of its explosive nature, and a hot tube M was substituted. This tube was made by winding about 20 feet of number 22 chromel wire around 20 inches of asbestos-covered 1/4-inch pyrex glass tubing ,and operated at 80 volts. On passing thru this, the ozone and the nitrogen pentoxide were decom posed and the nitrogen tetroxide was in part dissolved in the water pas- sing thru the aspirator. | | When a considerable portion of the nitrogen pentoxide crystals had disappeared the flow of the gas mixture was stopped bg shutting off the oxygen supply at the tank. The reaction bulb A) was then sealed at the constrictions I. About 20 cm. of capillary tubing of 0.05 to 0.1 om. bore between each of these constrictions and the reacting bulb preven- | ted any considerably diffusion of the hot gases into the reactiom vessel during the sealing off process. The pressure change was followed by means of an all-glass click gauge, F, as described by Smith and Taylor.» In 1 TO MANOMETER D I —o- — Og- Os H B € NA aA LA FIGURE 1 6. A thin bulb is blown in the end of a small pyrex tube, and is flattened in such a way that when the pressure difference between | | the inside and the outside of the bulb exceads a critical value the flattened portion of the bulb buckles in, causing a click. ‘This cri- tical pressure for any given bulb was reproducible to 0.2 um. or less. Three reaction vessels and click gauges were used in the course of the research. The first had a capacity of 320 ce. and a volume-to-surface ratio of about 1 cm. This was used in the first 14 experiments. At 35° the decomposition was so rapid that the time between the entrance of a sample of gas and its exit became a factor large in comparison to that of decomposition of the ozone; so in order to start with as high an initial ozone pressure as possible a bulb of 25 cc. capacity and a volume-to-surface ratio of 0.3 cm. was used. It was constructed as shown in the figure, ‘A’, in such a way that the gases had to traverse completely the space within the bulb and hence insure thorough sweeping out of the reaction vessel. This reaction vessel was used in experi- ments 15-24, The click diaphragm was broken in experiment 24; so a third bulb exactly like it was constructed and used in the rest of the experiments. In order better to observe the appearance of the brown colora- tion at the start of the nitrogen pentoxide decomposition, the reaction buld was silvered and then painted with optical black. Two small win- dows, J; 120° apart were then cut in this silver~-paint layer. The con- tents of the bulb were illuminated by shining light from a 100-watt daylight bulb thru one of the openings, and a spot on the silvered wall 7. opposite the other opening.was observed thru the latter. ‘The brown | color thus observed was much darker than that. seen directly thru the bulb because of the miltiple reflection which greatly lengthened the | light path. | It was found impossible to get a silvered surface that did not have a slight yellow coloration, due in part to the yellow cast of the glass itself; so the observation of the exact point at which the brown nitrogen dioxide started to form was not possible except in cases where the initial pressure of the nitrogen pentoxide was high. The reaction vessel was immersed in a thermostat kept constant to within 0.01° and not more than 0.02° from the specified temperature as determined by a thermometer checked against a standard thermometer. The pressure readings were made at intervals of from 1/2 to 5 minutes until ‘the nitrogen pentoxide decomposition was well under way. No stop- cocks were used in the gas train except in the exit tubes. However a ground glass joint .£) was used to connect the nitrogen tetroxide reser- voir to the rest of the apparatus. DeKhotinsky cement, vaseline, and paraffin were used to seal this joint for the various experiments. The nitrogen dioxide reservoir was removed between experiments and sealed off. A glass plug was then used to close the apparatus. In the first 24 experiments the oxygen flow was measured pre- vious to ozonizing by means of a flowmeter using Nujol as the manometric liquid. In these same experiments a capillary sulfuric acid manometer was used in connection with the ozone analyzer. In the remaining runs a flowmeter with mercury as the manometric liquid was used and the ozone analyzer was eliminated. 8, COMPUTATION OF THE PARTIAL PRESSURES All analyses were made from the pressure measurements. ‘The manometer readings were corrected for the "click constant" and the pressures thus obtained were changes to millimeters of mercury at 0°. zero time was taken as that at which the nitrogen pentoxide decomposi- tion started. To obtain this point the pressure was plotted against time using now the actual time and smooth curves were drawn thru the points. The point of intersection of the curve representing the ozone decomposition and that representing the nitrogen pentoxide decomposition determined the zero time as well as the pressure obtaining at that time. This gives a negative time scale for the ozone decomposition, which is used in all subsequent calculations. The ozone pressure at any time, t, ie given by the expression,Pp, = 2(Pp -P), where P is the pressure at time t and P, is that at time t = 0. The shift in equilibrium between nitrogen tetroxide and nitro- gen dioxide mst be taken into consideration in evaluating the partial | pressure of the nitrogen pentoxide in terms of ‘changes in the total . pressure. This was done by the graphical method of Daniels and Johnston, © which consisted of making a plot on a large scale (1 om. equivalent to 1 mm. change in preseure) of the change in the pressure of nitrogen pentoxide which corresponds to a change in the total pressure. Calculations for constructing the plot were made in the fol- lowing way. The total pressures at the time t = 0, and t are given 9. by the expressions ; Fo * Fo o, * Fo mos 7 8) P= Po, + Pxads + Puady + Pg, (6) where P, Op and Py Wp0s are the partial pressures of oxygen and nitrogen pentoxide at the time, + = 0, and Foo! PrOs? PyOo? and PHOu are partial pressures at the time, t. | Combining (5) and (6) and letting 4 P equal the change in total pressure and 4 Py Os equal the change in partial pressure of nitrogen pentoxide, and considering the change in the oxygen pressure which results from the decomposition of nitrogen pentoxide, we obtain | AP=P- Py = Pio, + Pron “24 Puoos . (7) Substituting Prod, * Prog * 2 +%) Proos in equation (7), where « is the degree of dissociation of nitrogen tetroxide, we obtain _ Bes (F+~) Pros , (8) The degree of dissociation, ~ , was then evaluated from the equilibrium expression {- xX a? = &@K PxeOs ; using for K the value obtained from Schreber's equation! log K ~ 2566 - log T- 9.132, and the plot described above, then construced in accordance with | equation (8). The partial pressure of the N20s at any given time is Pyo0s = Po Npds~ PNoOs .. The value of Py NoO, Was determined by allowing the reaction to go to completion as shown by the constancy of the total pressure | EXPERIMENTAL RESULTS 10. Ozone Blanks: ~- Two runs, one at 25° and one at 35°, were made in which no ni trogen tetroxide was admitted. The ozone-oxygen mixture was passed thru the apparatus just as it was done in a regular experiment. A freesing bath was placed around the nitrogen pentoxide trap to freeze out any condensible impurities and this was replaced by a water bath at room temperature to drive these impurities over into the reaction vessel. In this way any catalyst, other than nitrogen pentoxide, that might effect the decomposition would be detected, since the thermal decomposition of ozone at these temperatures is negligible. In neither case was any appreciable pressure increase observed as shown TABLE I T= 25° Po, = 35 mm. T= 35° Po, = 35 m. Time Pressure Time - Pressure Time Pressure min ram min mm min mn 0 buld sealed off 4O 742.9 O bulb sealed off 1.7 742.8 55 742.9 1.3 738.8 2.4 7h2.9 80 742.9 2.8 738.2. 3.1 742.9 120 742.9 47 738.1 7.5 743.0 290 742.9 10.0 737.65 . 19.3 742.9 4OO 7Th2.9 16. 137-7 25.6 742.9 26 brs. 742.9 25. 73767 0. 137-7 5 days 738.3 ‘An analysis of the ozone was made in each case. The high readings at the start of the 35° experiment may be due to a local heat- . ing of the gaseous mixture in the ends of the capillary in the sealing off process. ha Catalysts might stil be carried into the reaction vessel by the nitrogen tetroxide since this part of the apparatus was sealed off during these blank determinations, All substances used for sealing the ground glass joint were slowly acted upon by the nitrogen tetroxide; so that in the later experiments the nitrogen tetroxide container was finally sealed directly on to obviate any difficulty that might be aris- ing from this point.* No effect on the experimental results was obser- ved, nor was any effect observed as a result of using the different materials mentioned above for sealing the ground glass joint. The Experiments at Atmospheric Pressure: - The experimental procedure adopted made it most convenient to carry out the experiments at a total pressure of one atmosphere. Of the 32 experiments performed, 26 were carried out in this way, 15 of which were at 25° and the rest at 35°. The 6 runs under reduced pressure will be taken up in a later sec- tion. The first “experiments were preliminary ones and their results are not included in the following. Experiments 14 and 15 were discarded because of leaks, due to imperfect sealing off of the reaction vessel, which were detected in trying to obtain the final pressures. The click gauge broke in the course of experiment 24. Four typical experiments are represented graphically in Figure 2, two at 25°, and two at 35° shown in figures 2a and 2b, respectively. It was not feasible to use the same scale in both cases; so the time scale vised for the experiments at 35° is 5 times the other. In the original graphs a large scale was used for * All glass blowing then had to be done with the reservoir immersed in) a freezing mixture. The glass blowing was always done thru a phosphorus pentoxide tube, taking care not to introduce more water vapor than necessary from the flame in making the various seals. 12. pg ainbi4 sozquius Sowty ost oot os x os* & : f v 4 & > og [Loo TT a ot pa i + | 8 A . 5:4 . A Obl osl O9L | S “Wud “adn ssaid —. O82 13. Sapnuim “ou! | qz 2inbi 4 "ww Sainssaid | ° Ol 7 ine at ozZ | ; / of , F ly | oO vu ~ 0&2 aA of “ eal cA 7 oan FT | o- “4 0S. - 14, the pressures, 1 CM. ‘being equivalent to 1 m. change in pressure, and. _ in some cases a scale twice as large was used. It might be mentioned that the total pressures in experiment 21 have been lowered 25 m. in making the plot. In experiments & and 23, the initial pressures of nitrogen pentoxide were comparatively high, 139 and 69 mm., respective- ly, and, accordingly, the ozone decomposition curve is short because at these high pressures the rate of ozone decomposition was so great that it was Wery difficult to obtain the first pressure reading while an appreciable smount of ozone still remained. The initial pressures 6f nitrogen pentoxide were 17.& and 19.8 mm., respectively, in experiments 10 and 21. At low initial pressures of nitrogen pentoxide the difficulty in finding the point that marked the end of the ozone decomposition was increased, partly because pressure changes were small, making the experi- mental error in their measurement large and partly because the brown color of nitrogen dioxide did not appear sharply as mentioned in a pre- vious section. Table 2 includes data for all the experiments except those discarded for the reasons mentioned above. Time is given in minutes, taking as zero time the time corresponding to the break in the decompo- sition curve. In the cases where the pressure of the nitrogen pentoxide is omitted calculations were not carried out for its decomposition. In experiment 28 the final pressure reading was not obtained; so the initial pressure of nitrogen pentoxide was calculated from the specific reaction rate and from the measured rate of decomposition of the pentoxide. The values obtained from the last 5 experimental points checked within 15. 4 percent; and their average is certainly not more than 5 percent from the true value, judging from the precision with which similar calcula tions could be made in other experiments. In experiments 12 and 29 the points marking the start of the nitrogen pentoxide decomposition are very indefinite. Too small portions of the ozone decomposition curves were obtained in experiments 6, 7, 13, and 19 to be of value in any further calculations concerning the ozone decomposition. TABLE II ® Temperature = 25°C Experiment 5 Py NoOs = 23.7 mm. ain om, 53 "MeO t =P Pos PiOs 4o.0 3=—- 7. 7 11.6 . 102.5 753.4 19.4 36.5 743.8 7.4 132.5 755.0 18.1 32.5 744.9 5.2 168.5 756.1 17.2 29.5 745.6 3.8 182.5 156. 9 16.3 20.5 . 746.7 1.6 13.5 747.2 6 10.5 747.3 oy 7-5 - TH7.3 4 - 2.5 747.4 2 0. 747.5 0. 23.7 +2.5 747.9 23.4 75 = 748.1 23.3 12.5 748.3 23.1 -18.5 748.9 22.7 23.5 749.1 22.55 32.5 749.7 22.15 37-5 749.9 22.0 43.5 750.0 - . 21g 545 750.7 21.4 57-5 750.8 21.35 63.5 751.2. 21.05 72.5 °° 7H 20.9 HED « + onuw Ny oO e 2 e e e WW KDNAHAON HA-~I Mm NVNNRP RRR ARRSRE * e @ e « e e aAararar aw e e e IA EVES RY MA NWW OWAW NOU WO R~A~N NS OV °° ‘Experiment 6 Po No0g = 1101 mm. P 74U. 5 T4H4.9 745.1 745.4 746.0 747.6 748.4 749.4 749.9 70.9 751.6 T5e.3 753.3 15.1 756.2 757.3 758.5 760.9 | 763.1 764.0 (764.4 766.2 767.8 770.3 770.8 772.6 772.9 778.7 779.0 782.3 782.9 789.2 789.5 TABLE II (cont.) ‘Temperature = 25°C Py2Os 110-1 109.9 108.8 108.4 107.8 107.1 105.9 105.4 104.0 103.3 102.5 101.5 100. 6 99.5 97-3 95.2 94.3 93.9 92.1 90.5 88.0 87.5 85.6 85.3 79.0 78.7 74.9 74.2 67.0 66.7 0.0 ORPWA PU OANA oe o ee 7. 2 © © © «@ ° e e yr ARANVNUOWUNUE HORDE ARAEOMWVORA So Oy Fy fy ~ e Experiment 7 NoOs = 128.4 mm. P 743.3 743.3 743.2 743.3 744.1 ne 3 7TH4. 5 744.6 744.7 745.0 745.2 745.5 746.1 746.4 746.8 747.3 747.9 748.4 748.7 749.0 749.7 749.9 751.2 751.4 752.6 752.8 753.0 754.2 754.4 7155.2 755-4 758.1 758-3 762.3 762.4 766.21 776.2 776.4 788.0 728.0 807.0 854.6 oO w e e OFTONFRNARAAR 16. PNDOs 128.4 128.2 127.7 127.6 127.2 127.1 126.9 126.5 126.1 125.9 125.7 125.7 125.0 124.0 123.8 122.9 122.7 122.6 121.6 121.4 120.7 120.5 118.1 118.0 114.3 114.2 110.5 100.1 99.9 86. 63.7 0.0" OP Experiment 8 © NOs 7 138.8 t P 6.5 745.1 6.0 745.3 5.5 = 745.4 4.5 745.8 3.3 746.1 2.3 746.4 14 746.5 + 4 746.6 0.0 746,6 + .6 m6.9 1.5 747.3 2.6 747.6 3.5 748.1 4.6 9 748.5 6.3 749.2 73 749.6 8.1 749.9 9.0 750.2 9.9 - 750.4 10.8 750.8 11.5 751.2 13.2 751.6 13.9 752.0 15.3 752.2 17.1 753.1 18.2 753.5 19.0 753.8 20.1 754.1 21.9 754.7 23.3 755.0 24.2 755.2 25.1 755.6 26.1 756.0 27.1 75.3 28.5 756.6 29.1 756.8 31.5 757.4 33.6 758.1 35.9 758.8 41.1 760.1 46.21 761.9 "762.1 o” RPreMNw POON KFOKNENHNSG oo fe @ oo TABLE II (cont.) Temperature = 25°C No0s 138.8 138.8 138.6 138.3 138.1 137-7 137-3 136.5 136.3 136.1 135-9 135.6 135.3 135.0 134.7 134.5 134.2 133.8 133-5 133.2 133.0 132.8 132.5 132.3 132.1 131.8 131.5 131.0 130.8 130.3 129.8 129.1 128.1 126.5 126.5 Experiment & (cont. ) 138.8 Po NoOs = t P 50.9 763.0 51.6. 763.1 56.4 764.3 61.1 765.5 6159 767-8 66.5 766.9 72.0 768.2 80.9 779-3 89.9 772.5 91.7 772.9 101.9 775.0 111.7 777.0 200.4 793.0 201.4 793.2 365 814.3 562 830.8 1460 858.4 2730 82.7 eo 863.3 17. Np0s 125.4 124.3 123.1 122.8 121.6 120.8 118.4 116.2 115.8 113.6 111.3 a7 66.6 39.8 Tel 1.2 0.0 Experiment 9 Py No0s = 46.0 MMe t ?P 29.6 7ul 28.2 742.2 27.0 743.1 25.3 744.6 23.7 746.0 22.0 747.0 19.9, 748.2 18.5 748.9 15.1 749.9 14.0 750.2 12.2 750.8 10.7 751.0 a7 yale 7.6 TRL ed 6.7 751.5 5-8 = TLS 4.8 THT 4 7.8 - 1 751.9 0.0 7TR.9 + .3 752.0 34 752.9 54 752.9 6.3 753.0 7-7 753-2 10.7 753-4 14.9 753- 2 20.4 754.4 26.1 755.1 27.2 755.2 37-5 756. i 48.2 75704 59.3 758-5 68.2 759-3 70.2 759-5 9.4 761.3 115.1 763.3 116.6 165.5 160;1 766.8 290 774.6 4eg 780.6: 1083 79305 798.5 Os 21.2 19.4 17.6 14.6 11.8 sb LO oe es ® e e PRR PW EO oo o¢ e DOAN FRADEARANEOOL oo eo own BSBYBYBRSSEREGSEEE TABLE II (cont.) Temperature 25°C FinoOs 45,1 e oeeee . OA NUWWOWPr Alin hr OM AN ONO oe Experiment 10* Fo NoOs = 17.8 om t 66.7 “7 63.2 61.8 58.9. 5765 5567 53.9 52.0 49.7 46.8 Wy. 8 43.3 41.5 nNne ASSEGR A, O° e OW WNWOOF FN OO A au e P 740.8 741.5 742.5 743.2 744.1 745.8 746.4 747.3 748.0 748.8 749.7 750.7 75.5 751.6 752.0 752.5 752.9 753-1 753-3 753-4 753.6 753-8 753-9 Oz 29.0 27.6 25.6 24.2 22.4 19.0 ee rae Om 14.6 r=) aA e t @ e e e ONUIARQERNLUMNRQROUWU ARO ENOKHRAWWANW NW ~ e e Py o s © 18. N20s5 17.8 17.6 17.5 17.1 16.9 16.8 16.3 16.0 15.1 19. TABLE II (cont. ) Temperature = 25°C + _ Experiment 10* (cont.). Experiment 11 (cont. ) Po NoOs = 17-8 mm. Po NoOs = 35.2 om t P Fos; Prados t P Pos PNoOs 110.4 760.2 14.0 32.4 760.35 32.8 128.7 76057 13.7 42.1 761-0 32.3 146.9 761.3 13.2 52.3 761-75 31.9 190 762.7 | 12.1 66.4 762.7 31.0 22k . 763-7 11.3 80.8 763.85 30.2 o17 773-6 2.6 92.3 764.7 29.4 96.2 765-2 29.1 < 776.3 0.0 117.1 766.3 28.1 148.5 768.4 26.3 195.1 770.9 24.1 275-5 774.7 20.5 Experiment 11 301 775-7 19.5 Po NoOg 7 35-2 tm 432 780.2 15.0 35.0 745.5 23.0 oo 42 0.0 34.1 7h6.2 21.6 19 33.3 746.8 20.4 31.7 748.2 17.6 p? Lh: 16-7 Experiment 12 . T49~ : P = 9,5 mm. 27.9 750.7 12.6 0.N205.= 9-5 26.3 751.6 10.8 105.9 742.7 28.4 24.7 = 752.5 9.0 105.4 742.9 28.0 21.3 753.9 = 62 104.6 743.1 27.6 19.7 754.4 5.2 103.6 743.6 26.6 18.8 754.7 4.5 102.8 743.8 26.2 15-7 = 755-5 3.0 101.9 744.2 25.6 12.6 756.0 2.0 100.8 7h4.6 24.6 10.7 756.3 1.4 98.9 745.2 23.2 9.7 756.45 1.1 98.4 745.6 22.6 8.8 756.55 9 96.3 746.1 21.6 6.6 756.75 “5 93.2 747.3 19.2 3.9 756.85 33 90.9 748.0 17.8 - 3.1 756.85 33 88.4 748.8 16.2 0.0 757.0 0.0 35.2 85.4 749.7 yey 3.0 757.35 35.0 81.2 750.6 12.6 44 757255 34.8 78.8 751.2 11.4 5.0 © 757.65 34.8 15-3 751.9 10.0 6.7 757.85 34.65 71.7 752.7 8.4 8.8 758.05 34.5 66.5 753.7 6.4 24.7 759.55 33.4 59.9 754.6 4.6 TABLE I1 (cont. ) Temperature = 25°C ‘Experiment 12 (cont. ) . Experiment 28 (cont. ) + ?P Pos P05 t P Po, Py.05 5507 754.9 4.0 + 4 759.85 89.3 51.8 755.2 3.4 1.7 760.25 89,0 46.9 755.6 2.6 2.6 760.6 88.8 38.8 756.0 1.8 3.3 760.8 88.6 30.8 756.2 1.6 4.5 761.0 88.5 27.5 756.2 1.4 6.0 761.3 88.3 18.8 756.3 1.1 71 761.6 88.0 - 4.7 756.7 4 8.5 762.1 87.7 0.0 756.9 0.0 9.5 11.4 768.77 87.3 +11.7 757-2 12.8 763.1 87.0 26.7 T57+T 15.7 763.7 86.5 42.0 757.9 17.1 764.1 86.2 101 = = 759.8 21.3 765-1 85.4 164 760.6 22.8 7653 85.3 385 763-9 23.8 7655 $5.2 30.9 766.5 84.4 oo 769.0 31.9 766.8 84.1 42.7 768.85 83.5 Experiment. 28 59.5 771.8 79.9 90.0 177-95 75-2 16.7 750.45 18.6 ° 91.5 177-25 74.9 1§.6 751.65 16.2 104.3 779-15 73.0 14.7 752.75 14.0 106.1 779.4 72.8 14.1 753255 12.4 169 787.85 64.2 13.2 754.45 10.6 170 787.95 64.2 12.5 755.2 9.1 202 792.6 59.1 11.7 755.95 7.6 204 792.8 58.8 10.9 756.4 6.7 252 797-6 5304 10.2 | 756.9 5.7 254 797-6 53.4 9.0 T57 NS 4.6 8.1 757-9 3-7 6.5 758.6 2.3 5-7 = 758.9 1.7 5el 759-1 1.3 4.0 759.2 1.1 3.1 759.4 “7 2.1 759-5 5 1.3 759.6 3 - .6 759.7 1 0.0 0.0 89.4 759-75 Experiment 29* Py Nos = 18.0 ite + » t 78.8 77-6 AnPENaANon ve @ ee ¢ @ @ © # NA meen ww own ec ov Nee PSS 8 -P 749.0 75083 752.1 756.4 757-5 758.7 760.4 761.6 762.9 763.85 764.5 765.2 766.05 "767.05 767.5 767.9 768.2 768.4 768.7 769.0 769.25 769.3 769.5 770.05 770.0 770.2 770.15 770.45 770.9 771.4 772.05 773-6 19063 Os yo. 6 38.0 34.4 30.8 28.8 25.8 23.6 21.2 17.8 15.4 12.8 10.9 wo e eee CY ee oO . e TABLE II (cont.) Temperature = 25°C NoOs 18.0 2l. TABLE II (cont.) | Temperature. = 35° C Experiment 13 m Experiment 16 . P Fos F205 * P Poy NOs 2.2 740.3 1.2 14.5 747.0 20.2 1.5 740.9 0.0 13.7 748.5 17-2 -1.2 740.9 0.0 12.9 749.5 15.2 0.0 740.9 0.0 88.8 12.2 750.6 13.0 0.0 740.9 86.8 11.5 751.3 11.6 +1.1 742.0 88.1 10.3 752.8 8.6 2.0 748.8 87.5 9.5 753.3 7.6 2.9 743.9 86.7 8.3 754.2 5.8 2.0 744.9 86.2 763 755.1 4.0 4.5 745.5 85.6 6.5 755.6 3.0 5.1 745.9 85.3 5.8 755.9 2.4 6.1 746.8 84.7 4.1 756.3 1.6 7.8 748.0 83.8 3.4 756.5 1.2 $4 748.8 83.2 2.7 756.6 1.0 10.1 750.1 $2.2 2.0 756.7 8 11.0 75.9 21.6 1.2 756.9 4 16.2 755.1 78.3 - 4 757.05 wl 20.8 758.3 75-7 0.0 757.1 0.0 25.3 29.3 764.2 70.7 + .6 757-3 25.2 30.8 764.9 70.1 2. 757-9 24.8 106.0 79723 . 36.6 2 758.0 24.7 143.3 806.3 29.0 1 758.3 24.5 203.5 816.3 18.1 4.9 758.5 24.3 287.5 823.6 5.6 5.9 758.8 24.1 370.8 627.8 6.2 6.5 759.0 24.0 eo 832.1 0.0 9.7 760.15 23.2 10.4 760.25 23.1 11.1 760.4 23.0 13.3 760.15 22.5 15.0 761.6 22.1 19.4 762.7 21.3 27.6 764.5 20.0 28.1 764.55 20.0 28.9 764.6 20.0 29.5 764.6 20.0 37.2 766.1 18.9 38.6 766.4 18.6 51.5 769.05 16.6 52.6 769.1 16.6 84.6 774.1 12.5 119.4 777.1 10.0 155.4 720.0 7.5 23, -.. PABLE II (eont.) Temperature = 35°C Experiment 17 . Experiment 17 (cont.) 46.7 74u.2 27.1 - 2.9 758.05 46.3 745.0 26.1 0.0 758.05 0.0 4 45.6 745.5 25.1 + 8 7581 44.8 746.1 23.9 1.9 758.2 43.7 747.0 22.1 3.0 758.25 W167 2748.1 19.9 Jel 758.7 40.8 748.7 18.7 8.8 758.5 39.9 749.2 17.7 10.1 758.75 38.8 749.9 16.3 11.100 758682 37-8 750.6 14.9 12.1 758-85 36.8 7521.2 13.9 12.9 758-85 36.1' 751.3 13.5 19.4 759.3 35-4 751.75 12.6 26.5 759-7 34.6 752.1 11.3 27.3 75907 33.6 752.6 10.9 45.6 760.1 32.5 753.05 10.0 46.3 - 760.15 31.7 753-35 9.4 47.6 = - 76003 30.6 753-7 8.7 146 762.8 29.5 = 754.15 7.8 196 763.4 28.4 754.5 7-2 285 763.5 27.0 755.0 6.1 377 764.1 25.8 755.2 5.7 42 764.1 24.1 755-7 4.7 23.5 755-9 43 ad 764. 35 22.9 756.05 4.0 21.6 756.2 3.7 20.7 756.4 3.3 19.7 = 756.55 3.0 18.5 756.9 2.3 17-7 757-05 1.8 16.2 757.3 1.5 15-7 = 757-3 1.5 W.8 = 757655 1.0 14.0 75763 1.5 13.0 75765 1.1 12.2 757-7 7 11.4 757.75 6 10-3. 75709 +3 9.4 757.95 8.2 758.0 7-3 758.0 6.5 758.05 - el Experiment 18 t 25.3 23.6 22.2 20.3 18.8 17-5 15.8 13.4 13.5 12.0. 10.8 oe ° ' e WH NOW OW OW RNEN.D P MW OO e e e e * J e e e ‘ w ee oe oe oe ed EERBVAS SNES ENA PON oF rUNrHO e fte © @ © @ @ @ © © & 8 e NAAWwWoULf PUFF ROONMAFWA P 747.2 749.3 751.0 752.7 754-1 755-0 756.0 756.75 757-0 757.6 757-9 758.05 758.3 758.45 758.6 758-75 758.85 758.9 759.0 759.05 759.2: 759-5 759-75 759-85 759-95 759-95 760.15 760.75 760.9 761.05 761.15 761.25 761.45 761.65 761.7 761.85 762.25 762.25 763.75 765.15 7655 12.7 e e a e e DO NA OW WO F&F DE MO Kr MM NEN Temperature = 35°C Py20s 13-7 NRE RR ee - PABLE II (cont. ) Experiment 18 (cont.) ‘. 5-3 62.9 92.9 207.6 132 134 P Pos 66. ree 769.2 770-3 771.6 72-7 777-1 Experiment 19 P + e ° e e SHAW O DW AMRW ON EMH e © Nos = 77-5 mm 747.6 747.6 747.6* 74704 0.0 74S. 85 750.2 7H1-5 753-85 75504 757-2 75906 760.6 761.9 767-95 768.5 775-4 776.4 787.1 7H.3 79.8 794.1. 794. 55 799.1 09.4 - 809.6 811.0 811.6 829.7 24. P20 5 55-2 e SEWN SEP dion OO OLA OD RU we wow e oe wo 0.0 25, - PABLE II (cont.) Temperature = 35°C Experiment 20 Experiment 21 Py NOs 7 43-6 mm Po Nod, * 19-8 mm t P ‘ Pos PNDOs t . P Pos PDOs 5.2 = 749.6 5.4 17-2 749.3 23.8 304 = 752.1 2.4 15.9 751.3 19.8 71.2 752.1 4 12.9 755.5 11.4 0.0 752.3 0.0 43.6 11.3 757-05 8.3 #101 752.9 43.2 9.9 758.1 6.2 (24 753-4 42.9 8.5 = 75992 4.0 ar 754.1 42.4 6.9 75969 2.6 75 = - 754.6 42.0 5.6 760.6 1.2 5-5 = 755.0 41.7 4.5 76067 1.0 GeO = 75505 41 ot 3.7 7609 © .6 8.1 756.1 41.0 - 4 = 761.2 0.0 | 10-7 = 757-35 40.1 0.0 761.2 0.0 19.8 12.2 757-9 39-7 + .6 761.35 19.7 18.3 760.25 3769 2.8 761.9 19.3 21.3 761.5 37-0 4.5 762.3 19.1 22.7. 762.0 36.6 5.4 762.4 19.0 26.3 765.2 35-7 10.6 763.3 18.4 28.2 764.0 35.1 15.1 764.2 1707 32.4 = 765.7 33-7 21.6 765.5 16.8 36.6 766.8 32.8 23.1 765.9 16.5 39.7 767.8 32.0 24.4 766.1 16. 46.5 76925 30.6 42.3 - 769.2. 14.1 (62.0 = 773.85 27.0 65.9 772.2 11.9 $4.1 7787 22.7 118.3 784.35 17.6 135.7 786.7 15.4 oo 02.4 0.0 Experiment 22. | PS No0g * 15-7 mm t nN nN e a ODNNORAWEKNAHARONN AWA O MU * BER i aril ll eel adil sn TORY FUN m oo ¢ + Oo YM NVA UI AO e * e e e e e ° weer Na \O e OwWw KUO MRWOOKN LE ENN Fu P 736 738.9 740.6 742.2 743.9 745.7 T4725 748.25 749.5 7TH.2 TR. TH.7 750.8 70.8 750.9 750.9 751.0 751.0 751.1 751.1 751.2 7513 751.7 THL.95 752.05 752.2 752-3 752.5 752. 753-0 753.0 753.2 753-3 754.2 154 755. 756.1 757.0 767.6 767.6 | 768.9 769.3 771.6 * oe @ @ es @ NN 2 o 0.0 TABLE II (cont. ) Temperature = 835°C Experiment 23. PHOOs t Pp 5-3 T1301 4.4 718.1 2.9 720.0 - 4 721.5 6.0 721.6 + & 722.1 2.5 723.6 3-5 724. 3 4.8 725.2 7-0 726.9 8.3 727.9 9.3 728.45 10.7 729.35 13.8 731.4 17.6 733-55 25.6 738.05 33.1 7h2 05 5.3 TH 35 73-3 157-9 15-7 15-3 758.35 89.3 762.35 113.8 768. 35 115.1 768-65 oo 795-2 26. Na0s5 68. Gai 66.6 66.0 64.8 27. The Runs at Reduced Pressure: - The thermal decomposition of ozone is not only second order with respect to the ozone concentration but its rate is also proportional to the reciprocal of the first power of oxygen pressure.® To see whether oxygen had this inhibiting effect on the catalyzed decomposition some experiments were carried out at reduced pressure. Three experiments were made at a total pressure of 1/2 atmosphere and three at 1/4 atmosphere, two of which had too low initial nitrogen pentoxide pressures to enable the changes in pressure to be measured with any reasonable degree of accuracy, and hence to al- low the determination of the point of inflection on the curves. These experiments were all made at 25°, The experimental procedure had to be modified somewhat in making these runs. A mercury manometer, N, Fig. 1, was connected to the tube leading from the reaction bulb. After stop- ping the flow of the gas mixture the constriction in the inlet tube was sealed off. The stopcock, 1, shutting the manometer off from the rest of the system Was opened and the reaction vessel was partially evacuated thru stopcock,K, When the total pressure was reduced to 1/2 or 1/4 at- mosphere stopcocks,K and L,were closed and the reaction bulb quickly sealed off at the constriction in the exit tube. ‘The pressure was then followed exactly as before.. ' It was found that the click gauges would stand an atmosphere -Oxcess pressure on the inside of the bulb but rarely over 1/3 atmosphere excess on the outside. Hence the system outside the click gauge was always partially evacuated first. The results of the four experiments are given in Table III. 28. TABLE IIT Temperature = 25°C Experiment 25 Experiment 25 (cont. . a P P P t P P P min om. =m? 038205 129.0 4O7.2 18.8 61.0. 415.75 1.7 127.4 407.5 18.2 59.6 415.9 14 126.0 407.8 17.6 58.6 415.9 1.4 124.7 408.1 17.0 57.9 415.95 80163 123.8 408.3 16.6 57.0 416.0 1.2 122.7 408.3 16.6 56.1 416.0 1.2 121.3 408.6 16.0 53.8 416.0 1.2 119.8 409.1 15.0 52.1 416.1 1.0 118.6 409.35 14.5 50.9 416.1 1.0 117.4 409.55 14.1 50.1 416.15 9 116.4 409.7 13.8 49.1 416.15 9 114.9 409.9 13.4 48.3 416.2 8 112.0 410.6 12.0 45.0 416.2 & 110.0 410.9 11.4 42.3 416.25 7 107.8 41.05 11.2 38.9 416.25 7 106.4 511.5 10.2 32.8 416.35 05 104.6 411.7 9.8 31.7 416.35 05 103.0 411.95 9.3 21.8 416.45 3 101.8 412.2 8.8 20.8 416.4 4 97.1 412.6 8.0 10.0 416.5 2 93.8 413.15 6.9 0.0 416.6 0.0 6.05 92.7 413.35 6.5 +85 416.7 91.3 413.55 6.1 9.5 416.75 88.6 413.65 5.9 26.0 417.4 86.5 413.8 5.6 27.0 417.4 85.3 413.9 5.4 32.0 417.65 $2.8 41h.3 4.6 36.0 47.7 $1.0 414.6 4.0 37.7 417.6 79.8 414.6 Tie) 39.5 417.6 78.8 Wu.7 3.8 H.5 8 418.1 77-9 414.75 3.7 425 048.2 76.6 414.8 3.6 43.4 418.0 75-7 424.9 3.4 “y.7 418.0 74.8 414.9 3.4 5u5 8 8=— 4418 35 73-7 414.95 3.3 57 YES. 35 72.3 415.0 3.2 83 418. 35 71.0 415.1 3.0 100 418. 65 67.2 415.6 2.0 101 418.6 66.3 415.6 2.0 116 418.85 65.4 415.6° 2.0 117 418.9 63.5 415.7 1.8 235 420.4 -62.7° «415. 75 1.7 240 420.3 1.7 _" 416.6 61.8 = 5.75 _ TABLE IIT (cont. ) Temperature = 25°C Experiment 26 * . Experiment 27 * | ¢ P Fos PyoOs t P Pos PrOs 134.9 393.5 21.2 58 401.15 15.4 131.4 394.1 20.0 57 401.55 © 146 127.2 395.1 18.0 56.2 401.85 14.0 12.3 395.7 16.8 35-8 402.15 13.4 120.7 396.5 15.2 53. 402.55 12.6 114.3 397.7 12.8 50.6 403.35 11.0 109.1 398.65 10.9 48.0 4O4, 15 9.4 105.2. 399.35 9.5 46.0 404.65 8.4 101.8 399.7 8.8 43.8 405.25 7.2 96.15 400.6 7.0 41.6 405.65 6.4 93.0 00.85 6.5 38.5 406.3 5.1 89.7 401.3 5.6 36.5 406.55 4.6 83.7 401.65 4.9 31,2 407.35 3.0 75.1 4yo2.4 3.4 28.8 407.6 2.5 69.8 402.8 2.6 27.3 407.7 2.3 63.3 402.95 2.3 25.11 408.0 ‘1.7 59.4 403.0 2.2 22.6 08.25 1.2 55.2 403.15 1.9 18.4 408.35 1.0 50.6 403.3 1.6 15.3 4os.45 8 45.2 403.4 1.4 11.2 408.55 6 38.5 403.45 1.3 8.8 408.65 4 32.0 403.6 1.0 4.7 408.8 re 25.3 403.7 8 -1.8 408.8 1 18.6 403.75 “7 0.0 08.85 0.0 lay 10.0 403.8 6 + 8 HOS. 85 8.3 403.9 4 4.0 408.75 -1.6 404.0 .2 7.0 409.15 +4.7 4oh.2 9.8 409.3 6.3 404.3 10.7 409.35 14,1 4OK, 45 14.2 = 409.5 35. 404. 65 21.5 409.75 53 4Ou.9 23.5 409.85 6B 4O5.1 24.5 409.9 103 4O5. 5 27.3 0.0 135 406.2 36.0 410.2 150 © 406.6 38.5 410.3 182 4YO7.1 45.0 410.5 672 409.8 52.3 410.7 ©o 412.65 58.0 411.0 63.8 411.2 76.0 411.55 77.0 411.6 Experiment 27* (cont. ) * Every second or third reading over @ portion of a.run recorded. t P 88.0 412.05 89.5 412.15 102.0 412.4 103 412.45 116 412.85 118 412.95 133 413.35 139 413.3 162 - 414. 25 165 YLY. 35 270 416.4 368 418.15 oo sON26.2 Experiment 32 Py NoOs = 5.75 mm. 8.4 202.0 85.6 201.6 84.6 201.65 83.4 201.65 81.9 201.7 2.3 201.8 78.6 201.9 76.3 202.25 73-9 202.5 71.8 202.7 69.7 202.9 67.5 2031 65.5. 203.35 61.9 203.5 59.0 203.8 56.9 203.95 54.8 204.15 Rl.l = 204.3 48.7 204.45 46.1 204.6 42.1 204.7. 3965 204.75 35.8 204. 85 33-5 204.95 BRP PRP RMN EE Ua ON —~ rc e e e e e e _ + e cy .@ a RONWwWAAe A PF~ OMWUN BI RU Er mui Po 3 “NI 07 eo * e e ry . TABLE III (cont.) Pra0s . Temperature = 25°C + Prayreoryn e ONO FONFMuU ~ 14, 25 NnVr re Ww Mw Oo e « e e Omnmww -_08@ @ @ Nun OW NAA ° CEISIWEGYS B 205.05 205.05 205.15 205.3 205.4 205. 35 205.45 205.45 205.5 205-55 205.6 205.65 205.8 205.8 205.95 206.0 206.05 206.2 206.4 206.5 206.75 206. 85 206.9 207.2 207.2 207.2 207.25 207625 207.35 207-35 207-55 - 207.6 208.25 208.65 209. 35 213.05 Py20s 5°15 31. | In experiments 25 and 27 the finel pressure readings were | made after heating the reaction vessel to 60° for a period of. 14 hours and then thermostating again at 25°, allowing ample time for equilibrium conditions to be reached as shown by the constancy of the pressure read- ings. In experiment 26 the reaction was allowed to proceed for 40 hours. The reaction vessel was then heated as before, thermostated, and the pressure again measured. The pressure readings obtained before and af- ter this treatment agreed to within 0.1 mm. In experiment 32 the reac- tion was allowed to go to completion at 25°. THE NITROGEN PENTOXITE DECOMPOSITION Since the pressure readings were made at irregular time in- tervals and at very short intervals at the start of the nitrogen pent- oxide decomposition a graphical method rather than the usual interval method wag considered the best way to average the data,in obtaining the specific first order reaction constant, k,, for the decomposition of ndtrogen pentoxide. Log Pypo, Was plotted against the time in minutes, and k, determined from the slope of the straight line that best fits the points thus obtained. These. calculations were carried out only for the twelve best experiments, six at 25° and six at 35°, namely those for which the initial point of the nitrogen pentoxide decomposi- — tionwas most definitely marked. This, in general, was the casw when the initial concentration of the pentoxide was high. These results at 25° and at 35° are represented in Figures 3 a and 3 b,respectively. 32. sapnutw ‘awl | pe ainbly oor oot 002 oot aN Ng \ N NaN aN ANAL S| DRENNAN N a . \ Ne | \ f ONIS Ghai NEXT NP LR . XA LONE |. Ne INO No KINO \ Pe | M Sm | WEN ARRY TaN) AGN EF SS Ne PRA So7NY 607 33. sognuiw Soul yf qe ainbi 4 002 ost oo} _oS °: Na NS \ NO AN aw “AY aN NY NEN D5 A N Ne TNS 7 N oN NO No ve a New N aN Nal NN EN ae aw Se Sal + INN if | Rg NaS Sick’ gin. 6il \O N NI D. 9 ai & So*ny- 607] 34. In making the plots arbitrary log scales were used, the one at 35° being one-half that at 25°. On the other hand, the time scale _ for the curves at 35° is twice the other. The etraight lines fit the data well within the experimental error, and good agreement between the various runs is obtained as shown by Table 4.— TABLE IV T = 25° . T = 35° Exp. Py 4x00 x 109 Exp. P k, x 103 No. did ae No. 0 tn25 ‘nins4 6 110.1 2.00 13. 89,4 7.82 7 128.4 2.00 16 25.3 7.84 8 139 2.00 19 17-5 7-91 A] 46 1.92 20 43.7 7.81 10 17.8 2.03 21 19.8 7.70 11 35.2 1.97 23 69 7.81 Average 1.99 Average 7.81 These results are also in agreement with the values .00203 and .00805 found by Daniels and Jonnston.° They lead to the value, 24,970 cal/mol, for the energy of activation as compared to the aver- age value, 25,100 cal/mol, given by the above investigators for this temperature interval. 35- THE OZONE DECOMPOSITION | General Features of the Reaction: - Attention was next turned to the first stage of the decomposition of the gaseous mixtures, namely, the decomposition of the ozone. From the simple mechanism No05 —> NoOy + 302 > 2NOn + 800 (slow) (3) 2N0o + O03 — No0s + Or (fast) one obtains for the rate of ozone decomposition the expression -4Po/ dt = kPyo., (9) where kK is again the specific reaction constant for nitrogen pentoxide. From: these considerations one would expect that for any given run the rate would be constant, since the pressure of nitrogen pentoxide is constant as long as ozone remains. In two qualitative determinations Hiret> found the time necessary for the disappearance of the ozone to be in agreement with that calculated from the integrated form of (9) t = Po, / E,Pyiog- (4) In these experiments the initial prescure of ozone was, however, only 2.7 wa, and at low pressures the measured rate would not be expected to differ much from the calculated rate as will be shown later. This investigator also reported some qualitative experiments in which the initial pressures of the ozone were apprcximately known. Assuming 3 percent by volume (the lower limit given) ozone in the ozone-oxygen mixture, rough calculations have been made from equation (4) for the time necessary for the appearance of the brown coloration of nitrogen dioxide. And as shown in Table V, the actual time for the appearance of the brown color in Hirst's experiments was in general con- siderably shorter than that calculated from his equation. “TABLE V T Prog Pos kx 109 t +. mm mm min observed calculated . u7e 6 1 37 3 7 60° 47.5 g 170 re) 1.1 20° i — 9 1.2 © 160-170 160 33° 52 12 6 9 5 35° 23.5 6.4 7-8 T 35 The exception at 20° may be due to the fact that at this temperature the rate of formation of nitrogen dioxide is so small that several minutes would be required for the formation of a detectable amount of it. However, nothing is known concerning the amount of ozone used up immediately in oxidizing any tetroxide present at the start. In the colorimetric determination of the decomposition of nitrogen pentoxide carried out by White and Tolman the time necessary for the appearance of brown nitrogen dioxide was several times shorter than the value calculated as above. ‘Their experimental arrangement made it possible to detect very small concentrations of nitrogen dioxide, and hence observe quite accurately the time at which the ozone had just dis- appeared. The ozone aralysis was made preliminary to mixing with nitro- gen pentoxide; so allowance was made for the time necessary for the gas mixture to traverse the tube preliminary to sealing off. This was, how- ever, almost negligible at the temperature, 20°C, which was used in most of the experiments. In their experiments the initial pressure of ozone varied from 9.6 to 36.6 mm and that of the nitrogen pentoxide from 1.04 to 21 mm. 37 | The results of the present researchare quite in accordance with those of White and Tolman. Our method had the advantage that it . enabled us to follow the ozone decomposition throughout ite course. It was found that, although the rate of decomposition was much higher ~ than that. accounted for by (3), it always approached the rate predic- ted by this mechanism as the pressure of the ozone approached zero, and increased rapidly as the pressure of the osone increased, hence any expression for the rate of decomposition must reduce to (9) for zero ogfone pressure. One possibility is that the decomposition con- sists of two simultaneous reactions, the primary reastion,given by (3), and some secondary catalytic reaction depending on the pressure of ozone as well as on that of the pentoxide. Mathematically this is given by -APo,/ at = kPyiog + F(PyL06) Pos) (10) where F is a function of the pressures of both the ozone and pentoxide. The Me thod of Determining the Dependence of the Rate of the ——_ a Secondary Reaction on Ozone and Nitrogen Pentoxide: - As stated above F(Py,og° Pos) 18 in general a function of the pressures of both the nitrogen pentoxide and the ozone, but for any given experiment: the pressure of the pentoxide is constant,and the function is therefore de- pendent only on the ozone pressure, say proportional to some simple power, n, of it. . This would give . n F(Py.og? Pos) = €Puiog) ¥ Pose (12) The problem of determining the dependence of F on the partial pressures thus divided itself into two parts, the determination of the order, 38. first with respect to ozone, and second with respect to the pentoxide. The Order of the Secondar dary Reaction with Respect to Ozone: - Aseuning that the rate of the secondary reaction, which is given by F in expression (4) is proportional to the first power of the ozone pressure one obtains -aPo,/ at = + B Poy, (12) where « and @ are independent of the ozone concentration. Integrating with respect to Pos: log (HS +Fo,) = -@t+ log, (13) where the integration constant is evaluated from the fact that Pos = 0 when t = 0. Equation (6) can be put in the form stone (14) log v6 xe GR, = = -@G(t,t) =@r T being the time interval corresponding to a change in ozone pressure from Pig, to Po o3- For any given run the value %, = K,Py,05 is known from a kmowledge of the initial pressure of nitrogen pentoxide. The value of @ was first determined as follows. From the pressure-time curve for a given experiment was read off the time correspomding to a change of 5 mm. in the ozone pressure. For the experiments at 25° four intervals, corresponding to ozone pressure changes from 5 to 0 m., 10 to 5 m., and 20 to 15 mm. were used, provided the initial pressure of the ozone . permitted. At 35° only the first two intervals were used. The values thus obtained were then substituted in (14), and the resulting equation was solved for @ by a graphical method. 39+ The resulte thus obtained are given in Table VI. Subscripts refer to the interval number. TABLE VI Temperature = 25°C No. mm noma - min) min} min} min7 min) 5 23.7 12 .065 .086 -076 8 139 3 193 95 9 46 21 0113 .120 124 0119 10 17.8 29 .059 064 059 .054 .059 11+: 35.2 22 2114 123 .0915 = .088 204 12 | 9.5 | 28 O41 O42 .037 .0375 = .039 25 6.05 19 .0305 .029 027. .026 .028 26 6.4 21 030 031 .029 .027 .029 27 14.4 15 -065 .059 O85 .O57 28 g9 19 -160 .187 .189 .178 2gt 18 41 053 .057 055 050 054 3 5.75 725 .O4f 04 Temperature = 35°C 16 25.3 253 227 » 240 17 yy 2105 084 O94 18 13.7 148 127 .138 20 43.7 - 393 393 21 19.8 -238 .198 .218 22 15.7 .188 173” .180 23 69 “415 690" 55 *In these experiments the end of the ozone curve was very indefinite. *The time interval from which this value is obtained is only .9 min. 40, It will be seen that the values of @ fall off as the pres- sure of ozone increases indicating an order with respect to ozone slightly lower than the first. This falling off is greatest where the initial pressure of the nitrogen pentoxide is low, and hence where the reaction rate is slow. Experiment 27 with an initial nitrogen pentoxide pressure of 14.4 mm. shows the greatest effect where @ falls off by 1/3 its value, However, the value of @ obtained from the first interval is not as good as that determined from the other intervals, first, because at low ozone pressures the rate is largely determined by ~ , and second, because of the difficulty in determining the time at which the ozone reaction ends. An error made in this determination especially in the experiments where the rate is slow would not lead to appreciable error in the pressure at this point and hence would not greatly affect the values of for the other. intervals. | In order to obtain a better average of ( , the following method of calculation wes also used. ‘The average value of (3 as de- termined by the interval method was substituted into the left-hand side of (6), and the quantity log(% + Pe,) was then plotted against -t. The average slope of thig line was then taken as giving a corrected value of @ . At higher values of P 3’ e “becomes small in comparison $0 an error in the selection of @ becomes negligible in the sum. The values of @ thus obtained are tabulated in the succeeding section. Figure 4 illustrates graphically the results of 4 experiments of which 11 and 25 were carried out. at 25° and 17 and 18 at 35°. The decrease _ in the value of (8 with increasing ozone pressure is again show in 4. Sopnuiw ‘out 4 ainbly 0-l + oz Ob- of- oz ol- =p [Lt gS arte — du Po oP Ye leaot | | oa os at obo = ~~ ae )607 2, the experiments at lownitrogen pentoxide pressures. In experiment 17 the initial pressure of the pentoxide was only 4.4 mm. ‘The irregular- ity of the points at the lower end of this curve is due to the large experimental error in determining the time corresponding to a given “Ozone pressure for these slow rates. The Order with Respect to Nitrogen Pentoxide: - The next step in determining the form of F was to investigate the dependence of on the nitrogen pentoxide pressure. As was done in the case of ozone, as- sume Q proportional to some power of the pentoxide pressure @ = kePh og: (15) Since the value of B was determined over nearly the same ranges of ozone pressures the order, n, found in this way is almost independent of any small deviation of the order assumed with respect to ozone from the true order of the reaction. To determine the value of n the logarithm of (R was plotted against that of Py5O5! the slope of the line obtained giving the value of nw Figure 5 represents a plot made in this way. The lines, drawn in with slopes equal to 2/3, fit the data fairly well at both 25° and 35°. 8 then takes the form, = 2 | p = kp Pye? - (16) kp was then calculated from this expression and its value for the various experiments together with the value of 3 found in the preced- ing sectdan is given in Table 7. Log @ C 43. © PNG \ oN 0 | | me 26° 5° aS t) IM fe} — SS NM I -0 | ~ S {-O 5 | 20 | Log Pnzos Figure 9 TABLE VII Temperature = 25°C 2/3 3 Kp. . Pp P ne n205 Np05 mmm? ¢72 mre! 3 ol 5 23.7 8.25 0.0% 0.0097 g 139 26.8 -210 0078 9 46 12.8 0117 -0091 10 17.8 6.83 2060 0088 11 35.2 10.8 .102 -0094 12 9.5 — ug -O40 0089 25 6.05 3.32 030 -0090 27 14.4 5.93 0058 -0098 2g 89 20.0 2174 - 0087 29 18.0 6.88 2055 ~0080 32 5.75 3.21 ae) 012+ Average 2089 Temperature = 35°C 16 25.3 8.60 219 023 17 4ue4 2.92 rae) 030 18 13.7 5.72 138 024 20 43.7 12.4 035 .028 21 19.8 32 22 +030 22 15.7 228 172 027 23 - 69- 1.59 043 -027 Average C27 + Experiment 32 was carried out at a total pressure of one-quarter atmosphere. This value of kp is not included in the average. The Effect of Oxygen: - If the secondary reaction involves some chain mechanism it was conceivable that the oxygen might inhibit the reaction by deactivating thru collisions the activated molecules participating in the chain, thus decreasing the number of ozone mole- cules decomposed per chain. However, no increase in the rate was ob- served in three experiments in which the oxygen pressure was approxi- 45. mately halved. One experiment in which the total pressure was 1/4 at- mosphere showed a 1.35-fold increase in the rate as shown ‘in Table 7. “In this experiment the initial pressures of both ozone and nitrogen ‘pentoxide were low, 8, 3, and 5.75 millimeters, respectively, making it difficult to determine the point of inflection, and hence, the value of kp. From the above results it can be definitely concluded that the rate does not have any large dependence on the oxygen pressure, as is the case in the thermal decomposition of ozone, where the rate is in- versely proportional to the first power of the oxygen pressure. DISCUSSION OF RESULTS The rate of decomposition of ozone in the presence of ni- trogen pentoxide may hence be given by the equation 2/3 - 4 Po,/ at = ¥,Py 9. + KoPy.Og Pos (17) over a range of nitrogen pentoxide pressures from 6 to 129 um at 25° and from 4.4 to 69 mm. at 35°, and for ozone pressures up to 25 mm At high ozone and low pentoxide pressures the rate falls off from that first order with respect to the ozone. The value of kp increases 3.3 fold for the 10° rise in temperature as compared to the increase of 3.9-fold for k; over this range. No theoretical interpretation has been made to account for the 2/3 power with respect to the pentoxide. The fact that the order with respect to both the ozone and pentoxide falls below unity when the rate is slow suggests inhomogeneity of the reaction, a wall reaction of lower order taking place. However, the fact that changing the surface- to-volume ratio three-fold in the reaction vessels used had no effect on the rate, and also that the order with respect to nitrogen pentoxide “is lowered the same amount at the two temperatures are arguments against any appreciable reaction taking place on the walls. It might be poseible to fit the data over the range of pres- sures studied with an expression of the form - APs At = Py og + (Pxog)(Fos)/(aPu05 + Pos + Fo, + 4) (28) where the presence of PyoOg and of Pp, in the denominator would lower the order with respect to these variables, and the term CPO, would lead to an inhibiting effect of oxygen for which there is some evidence in U7. experiment 32. ‘The relative values of a, b, c, and 4 would then de- termine the amount by which the order with respect to the various pressures is lowered. An expression of this type can be derived from the following mechanism. Na05——» NoOy + 302 (a) NoOy + Os -—> NoOs + Os! On! + O03 —> 03! + Op (b) O3" + 03 —> Oo! + 205 (c) Oo! + 03 —> Op + O35 (a) (19) Oo! + NoOg —» Op + No05 (e) O2' +> 02 (g) This gives a chain mechanism which is almost certainly neces- sary to account for the large increase in the rate of ozone decomposi-~ tion over that at low pressures (approximately 15-fold at 20 mm. ozone pressure). In step (a) ozone oxidizes the nitrogen tetroxide, formed in the pentoxide decomposition, with the formation of an active oxygen molecule. From the heat of dissociation of ozone 03 —> 3/2 02 + 34,000 cal., (20) and the heat of formation of nitrogen pentoxide from the tetroxide and oxygen . No0y + 302 —> NoOs + 2690 cal., — (21) it is seen that there is available approximately 37,000 calories for the activation. In the next step (b) an activated oxygen molecule collides with en ozone molecule resulting in an interchange of the 4g, energy of activation. The excited ozone molecule thus formed can collide with a normal ozone molecule giving again an activated oxygen molecule (c). This molecule can then collide with ancther ozone mole- cule with a repetition of the above process, or it can become deacti- vated by collision with any of the molecules present, as shown by steps (d), (e), and (f), or by a unimolecular decay, as in (g). Equation (18) can be derived from the above as follows: Let k,, ko, ks, etc. be the rate constants for the reactions (a), (b), (c), ete. Ozone is used up in steps (a), (b), and (c) the rate being given by | - d(Os)/dt = ky(No05) + ko(03)(02") + k3(03") (03), (22) where (03), (Np05), etc. are concentrations of the ozone, pentoxide, etc., respectively. The rate of change of O3' is a(O3")/at = kp(02') (03) - k3(3') (03), (23) and that of Oo!, A(O2')/dt = k1(Np05) - ko (02') (03) + ks (03') (03) - ky(02")(03) - k5(02')(N20s) - kg(O2') (02) - k7(02'). (24) Since (02') and (03') are very small, their rates of change. can be put equal to zero. From (23) we then obtain the equation ¥2(02') (03) - k3(03')(03) = 0, (25) or (031) = *2_(05"). (26) ky: 49 * and from (24), after substituting for (03') its value in terms of (02') given by (26), ie, (N20) - key (O2") (Ds) - ks(Oz") (Nz05) - 4G(02") (Oz) - e702") = 0 | | | (27) Solving. for (05') k, (NoOs) (02) = ky(O3) + kg(No05) + k¢ (02) + ky ° (28) Substituting (26) and (28) in equation (22) there results a(O3) 2k 1kp (NoO5) 03) a ~ a =k (Np05) + is) + Kg (No0s) + a) rn ke, 4 (29) which can easily be put in the form (18). If any of the last four steps in (19) were ineffective in deactivating the Oo! the rate for that reaction would become zero and the term corresponding to it would drop out of the denominator of the last term of (29). | Other mechanisms might be worked out, possibly involving the ozone-ni trogen pentoxide complex, reported by Warburg and Leithauser to be present in very small concentrations in mixtures of ozone and the pentoxide, as an intermediate product of the reaction; but no attempt in this direction has been successful. This research was suggested and supervised by Dr. Richard C. Tolman, to whom the author is greatly indebted. The author also wishes to extend his thanks to Mr. William . Ure, who started the research, working out the general method of procedure, and to Mr. Warren P. Baxter for his assistance in carrying out the experiments. SUMMARY A method of determining the rate of decomposition of oz0ne= nitrogen pentoxide mixtures, which consists of follawing the pressure change by means of an all glass "click" gauge, is given. The decomposition curves were found to consist of two parts, the firet representing the decomposition of ozone and the second that of the pentoxide. A sudden 3-fold increase in the rate marks the start of the pentoxide decomposition. The specific reaction rates for the first order decomposition of nitrogen pentoxide at 25° and 35° were found to agree well with the results of Daniels and Johnston. At high ozone pressures the decomposition of ozone was found mach faster than that required for the oxidation of nitrogen dioxide formed in the decomposition of nitrogen pentoxide, but approached this predicted rate as the ozone pressure approached zero. An expression for the rate in which the reaction was divided into two parts, one depending on the pentoxide pressure alone, and the other on both the pentoxide and ozone pressures was worked out. In the expression giving the second reaction rate the order is found to be 2/3 with respect to the pentoxide, and approximately first order with respect to ozone, falling off where the pentoxide pressure is low. The total pressures were reduced to 1/2 atmosphere with no appreciable effect. One experiment at 1/4 atmosphere shows a slightly increased rate. Another form of rate expression,for which a mechanism is given, is suggested. 1. F nm ~ oO ww _@ ° e e REFERENCES (a) Daniele and Johnston, J.Am.Chem.Soc., 43, 53 (1921); (b) Hirst, J.Chem.Soc., 127, 657 (1925); - (ce) White and Tolman, J.Am.Chem.Soc., 47, 1240 (1925); (a) Hibben, ibid., 50, 940 (1928); and others. Daniels, Wulf, and Karrer, J.Am.Chem.Soc., W4, 2402 (1922). see 1 (b). see 1 (c). Smith and Taylor, J.4m.Chem.Soc., 46, 1393 (1924). see 1 (a). Schreber, Z.physik.Chem., 24, 651 (1897). Wulf and Tolman, J.#m.Chem.Soc., 49, 1202 (1927). Warburg and Leithauser, Ann.Physik, 23, 209 (1907).