The Ammonia, Carbon, Hydrogen Cyanide, Hydrogen Equilibrium, and the Free Energy of Hydrogen Cyanide Citation Badger, Richard McLean (1924) The Ammonia, Carbon, Hydrogen Cyanide, Hydrogen Equilibrium, and the Free Energy of Hydrogen Cyanide. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/2ZMQ-YC04. https://resolver.caltech.edu/CaltechETD:etd-05132003-153829 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): Unknown, Unknown Thesis Committee: Unknown, Unknown Defense Date: 1 June 1924 Record Number: CaltechETD:etd-05132003-153829 Persistent URL: https://resolver.caltech.edu/CaltechETD:etd-05132003-153829 DOI: 10.7907/2ZMQ-YC04 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 1765 Collection: CaltechTHESIS Deposited By: Imported from ETD-db Deposited On: 14 May 2003 Last Modified: 03 Oct 2019 23:11 Thesis Files Preview PDF (Badger_rm_1924.pdf) - Final Version See Usage Policy. 1MB Repository Staff Only: item control page

Galifornia Institute of Technology Pasadena, California THR AMMONIA, SGARBON, HYDROGEN CYANIDE, HHDROGEN EQUILIERIVM, AND THE RAR BNARGY OB HYDROGEN CYANIDE Thesis for Degree vboctor oz Philosophy Richard l.Badger 1924 | THE AMMONIA, CARBON, HYDROGEN CYANIDE, HYTROGEN EQUILIBRIA, AND THE FRYE BQERGY OF HYDROGEN OYANTDE . By Richard iM. Badger Thesis presented to the faculty of the California Inatitute of Technology in partial fulfillment of the requirementa for the degree of Deator of Philosophy June, 1924 THE AMMONIA, CARBON, HYDROGEN CYANIDE, HYDROGEN FQUILIBRIIUM, AND THE FREE ENERGY OF HYDROGEN CYANIDE By Richard M. Badger Introduction Probably the first synthesis of hydrogen cyanide was effected by Clouet? by passing amuonia over wood charcoal at red heat. The reaction involved in this experiment is: NH3 + C(s) = HON + Hp. This reaction has subsequentiy been quantitatively studied; and its uses has frequenbly been proposed for the coumercial synthesis of hydrogen. cyanide. Tras Berguann” found that even at 1100° the reaction was measurably slow, but that a considerable prorortion of ammonia decomposed into nitrogen and hydrogen. The yield of hydrogen cyanide increased with temperature; and at 1300° the greater part of the ammonia waa converted inte cyanide. Lance? obtained evan larger yields, and found that where the gases were diluted with nitrogen a portion of this gas was fixed as cyanide. An elaborate series of experiments batween 720° and 1120° was conducted ty Yoorkelius+, who found that the yield of hydrogen cyanide was favored by the higher temperatures, faster rates of flow, and dilution of the gas mixture with illuminating gas. ‘The character of the catalyst has a large influence on the decomposition of the ammonia and hydrogen cyanide, porous materials being very effective. All of these in- vestigations were, however, of the nature of rate measurements rather than of equilibrium experiments. TClowat, Ann. de chim., 11, 30 (1792). ® Bergmann, Je f. Geabel., 39, 117 (1896); see Chem. Zentr., 49, 943 (1896). 3 tence, O. r., 124, #19 (1897)- 4 Vosrkelius, Dissertation, Hanover, (1909); Chem. Ztg-, 33, 1078, 1090 (1909); see C. A., 4, 1653 (1910). -2- The reaction involved in the work just mentioned seems very woll euited in many ways for a study of the stability of hydrogen cyanide at moderately elevated temperatures. ‘The equilibrium-constant becomes measurdle at avout 500°, and a combination of this with the reliable work of Haber and his asso- Giatesa on the dissociation of ammonia enables one to calculate directly the equilibriun between hydrogen cyanide and its slements, and hence its free anergy of formation. I+ 1s true that at temperatures where the conatant vegins to become measurable amoonia 1s nearly completely dissociated so that the ultimate equilibrium mixture would contain very little ammonia, and a mera trace of hydrogen cyanide with a great excess of hydrogen and mitrogen. The problem of this work was therefore to find conditions under which the ammonia dissociation is slow but the desired equilibrium is rapidly reached, 60 that it can be studied as a metastavie stats. The invastigation was made at the suggestion of Professor A. A. Noyes, to whom the author is indebted for many valuable suggestions. The work waa assisted by a grant made to Frofessor Noyas by the Carnegie Institution of Washington. a, oo Se \ es an Ga EGOS IGN He eee OVO SLL OE EEG ARH [| ECON SS eg | se FL NCR CATING Aad nN t Ue aT een i N FRCS SEO SOU US GAIN AU A GS CUR NEE S| AE RUS IOAN . _ Apparatus and General Procedure The Apparatus. - ‘Tha schematic diagram of the figure accompanying, showa how the experiments were conducted. <A constant-flow method was used— a mixture of gasea belng passed continuously over a heatei layer of charcoal contained in a silica tube and the resulting mixture being absorbed or collected for analysis. The gaseous mixture was diluted with nitrogen, this being found more convenient than to work under reduced preasure. The left side of the diagram reprasents the arrangement for mixing the gasaa to be passed into the reaction tube. The ammonia waa supplied from a cylinder, and the nitrogen was prepared by removing oxygen from the air. Into this latter gas could be introduced any desired proportion of hydrogen cyanide by the use of the saturator S, which contained an acid solution of scodiun cyanide of suitable concentration; a by-pass allowed the supply of hydrogen cyanide to be cut off vhen desired. Capillary flow meters M were provided for con- venience in controlling the gas mixtures. the charcoal was confined between two graphite plugs in the center of @ long ailica tube within the furnace F. A thermocouple junction was imbedded in the charcoal, the junction and leads L being contitined ina small porcelain tube for protection. The reaction mixture of gases waa rapidly withdrawmm from the catalyat through a pyrex capillary C, and passad to the absorption and collection apparatus. The artenia and hydrogen cyanide was absorbed in distilled water by the use of two absorption bottles A, only one of which ia shown in the diagram. The gas washing spiral, as indicated in the sketch, was so constructed aa to have a very emall dead space, and it was removable so that the titrations Could be carried on right in the absorption bottles. In runs 1 — 4 a small olen Uetube containing pure adda line slightly moistened waa located between the reaction chamber and the absorption bottles end served to collect all the cyanide. The gas from the second absorber was dried by passing it through a apiral sulfuric acid washer D and a phosphorus pontoxids tube. It then flowed through a device H, for determining the hydrogen content by thermal conductivity. This method, developed at the Bureau of Standards, seened especially eultable aa the gaa at thie point contained only nitregen and hydrogen, and ita thermal conductivity could be readily compared with that of the gas after the hydrogen had been removed by heated copper oxide (conteined in the furnace 0 of the diagram). The volume of the nitregen renaining was determined by weighing the water it displaced. D Weaver, Palmer, Frantz, Ledig, Pickering, J. Ind. Ing. Chem., 12, 359 (1920). ~~ The Charcoal. - In runs 1 = 4 inclusive a vary active charcoal supplied by the Fixed Nitrogen Research Laboratory was used. This was found +o te very effective in establishing the desired equilibriwn, and yet did not decompose the amonia at a repid rate. This was to be expected , ginee eharceal ia not a good catalyat for the ammonia ayntheais. In runs 5 and 6 the charcoal was further purified by heating i+ in a stream of chlorine at 800° for some hours, and then washing it with a stream of nitrogen under redueed pressure. The activity of the carbon was somewhat decreased by this process. In all cases the carbon was evacuated, and washed with nitrogen at about 500° before using, and the reaction mixture was passed over it for about half an hour before the iesuing gases were collected. In runa 1-4 the charcoal layer was 18 om. long and 2.2 om. in diameter; in rune 5 and 6, it was 0.5 cm. long and 2.5 om. in diameter. inalytical Methods Analysis of Amzonia. - The ammonia was titrated in the absorption vesasels with sulfuric acid. Analysia of Cyanide. - Very small amounts of cyanide had to be determined, since it waa necessary to work at temperatures where the equilibriwa is far in the direction of ammonia. In rune 1 - li, where the cyanide was absorbed on soda lime, a procedure similar to that recommended by Lavialle and Varemne was used.6 The eoda lime containing the cyanide was transferred to a casserole and moistened with a solution of sodium polysulfide. The mixture was evaporated to dryness and the resulting thivoyanate was dissolved in a little dilute sulfuric acid solution and g Lavialle and Yarenne, J. pharm. ohim., 17, 97 (1918); see C. A., 12, 1159 (1918) a slight excess of calcium carbonate then added. After filtering and eveporating to dryness the solution, the residue obtained was disaolved ina little dilute sulfuric acid and titrated with 0.005 NH. silver sulfats solution, using ferric sulfate as an indicator. As the end-point was found to be greatly influenced by variaus conditions, 1¢ aeema possible that these determinations may be considerably in error, but no more than by 15%, In the last two experiments the hydregen cyanide and ammonia were absorbed in the same vessel; and, after titrating the emconia, sodiwm bicarbonate was added and the cyanide titrated with 0.003 N. iedine solution, with ataroh as an indicator. This method was calibbated under the conditions prevailing in the experiments and gave consistent results. Probably the separate determinations were in error by not more than 5%. Preilwinary Experimenta Before attempting a study of the equilitrium the possibility of side reactions was investigated under the conditions to be used. Of these the two most prodadle ones are the formation of methane and of amines. By the reduction of hydrogen cyanide at 110° in the presence of platinun black, methyl amine ia produced. ! “ith nickel as a catalyst at 250°, ammonia, methyl, dimethyl, and trimethyl amines are produced. © Experirents failed to show the formation of a detectable amount of methane at 500° when hydrogen was passed over the charcoal. A gas containing about 30% hydrogen cyanide and 70% hydrogen was then passed over the charcoal wider the conditions later employed in the equilibrium experiments. When the gas issuing from the charcoal was passad through water, the rasulting solution gave « strong test for ammonia with Jessler‘s reagent, while a portion acidified with hydrochloric acid and evaporated to dryness failed to give the test for amines with chlorinal.” This teat was found to give a very distinct reaction with as small a quantity as seven milligrams of dimethyl-amine hydrochloride. The Equilibrium Experiments The accompanying table gives the results of six equilibrium experiments. In half of these the gas introduced into the reaction tube wes a mixture of amvonia and nitrogen. in the other cases the equilibrium was approached from the hydrogen oyanide side by adding this gas to the ammonia mixture in from three to four times the concentration found after equilibriwn was attained. Hydrogen was not added, as this was supplied by the decomposition T Devas, Ann., 128, 201 (183) & Sabatier and Senderens, ©. r., 140, 483 (1905) 9 Taalpatani, Chen. Zentr., 79, 299 (1908) of the amvonia. It was not feasible to ay roach equilitrium starting with mixtures of pure hydrogen cyanide and hydrogen, either because of poisoning of the Catalyst or of some peculiarity in the rate of reaction when the concentration of the former gas is larga. After bringing the charcoal to temperature in a stream of nitrogen, the anuenia wixture wae passed over it for thirty minutes or more before the recetion gases were collacted for analysis. The rate of flow and the tenperature were kept practically conatant during each run. The first row of the table indicates the total duration of a run, the second the temperature on the absolute scale, and rows three to 91x give the analysis of the total reaction mixture collected during a rum. In row seven is given the total pressure in the reaction chamber, and in row eight the equilibrium constant K, at the average temperature of the experiment, calevlated by the equation: Rou, 2 new PW, In the final row the constants hve been corrected to 2CO°A as described below. Table Expt. no. 1 2 x ye 5* 6 Time in mins. ll2 50 120 130 160 eho Abs. temp. 201 611 807 793 785 803 Millimols Hp QO 535 0.756 0.439 0.686 0.084 0.103 Millimole HCN 0.0205 0.0462 0.079 0.055 0.065 0.073 Millimels MH 27-3 Wet = 380 5463 BE 28 Millimols Ng 23.44 59.6 = Oe BRS 3203 5B Pressure ( xn.) 747 Tay 745 745 TUT 747 K. 10° 17 43000 BG 3.5 3.7 E gopeat 20° 734 5.0 O.7 = Ge 59 363 Neote- In the experiments indicated by the asterisks equilibrium was approached from the ammonia side. ~1C~ A few experiments at higher temperatures indicated that the equilibrium changed as was 40 be expected from the approximately known haat of reaction, bat at these temperatures the results were too erratic to lead to a more accurate determination of this heat change. Some experiments were attempted to determine the relative rates at which equilibrium was established and at which ammonia and hydrogen cyanide decomposed. The difficulties of exuct analysis uade 1+ impossible to separate the effects of the concurrent reactions. It was found that the rate at which hydrogen cyanide combines with hydrogen dees not increase with the firet yower of the hydrogen cyanide partial pressure, but sven when nitrogen containing considerable cyanide was passed over the catalyst, the rate st which the hydrogen united with the cyanida was large in comparison with the rate at which it was produced by the déconposition of the cyanide. “he host conclusive reason, however, for believing that an equili>rian was really obtained 1s that the "constants" are not affected by the direstion of approach to squilibriw. #lle The Free Energy of Hydregen Cyanide The available hes} data relating to hydrogen cyanide aré meagar and probably not very ateurate. For the wolal heat of combustion of this gas Thomsen gives 158,600 calories and Berthelot+” 159,300 calories. These values are in fair agreement and sre probably more accurate then the result obtained by more indirect methods. The mean value 15€,900 calories, combined 11 and the heat of with the heat of combustion of graphite (94,250 cal.) formation of water (68,330 oal.)*? givee 30,500 calories for the heat-consent of LHON at 16°. Heat capaolty date are lacking; but 1+ soema reasonable te secume that hydrogen cyanide has nearly the saue values as carbon dioxide. Like this gas it aparently exhitits the absorption spectrum of a distomic gae in the infra red, bot like thie gas 1+ probably alao picks up energy wore rapidly at elevated temperatures than the diatomic gasea. The molal heat-oapacitiee assumed for hydrogen, nitrogen, and graphite are those given by Lewis and Randall. A combination of thease data yields for the heat-content of hydrogen cysnide thie formula: H= 30,600 - 0.60 T + 0.00068 T® ~ O.00CC0022 T . This gives for the hest-content at S0Q° A the value 30,400 cal. Haber?3 in his suneary of the measurenents on the amronia equilibriua gives for the heat-content of ammonia a formule which leads to the value -13,000 calories 10 Berthelot, Ann. chin. phys., (5) 23, 252, (1661). 11. Roth and Wallach, Ber. deut. chem. Ges., 46, 896 (1913). 12 Lewis and Randall, "Thermodynamica", McGraw-Hill Book Co., New York, 1923, y 477. 13 Haber, Z. Electrechem, 20, 597 (1914). 12 at 800° A. Combining theese data we obtaln the value 43,400 cal. for the “drerease in heat-content attending the reaction 3H; + ¢ (s) = HCN + Hp. Aesuming this value to bs practically constant over a small temperature range, it was used to eorrect the tebuiatad values of theequilibvciun G Tha constant of this reaction to 800° A, giving the mean value 5.8 x 107 free energy inorease attending the raaction ia thus 19,200 cal. Haber gives a tommla for the calculation of the amrionia equilibrium constant over a range of temperatures. Probably the value for the free energy of ammonia at 800° A, 9,220 cal. as calculated by lta use, is not greatly in error. Thuse data leud to the value 24,400 owl. for the free energy of hydregen cyanide gas at 00° A. Combining this with the heat data mentioned we obtain for the free energy of this gas aa a function of tenperature: E= 30,600 + 9.60 2 ln T - 0.0006€ T? + 0.cooccOl] T7- 6.3 T. This leads to the srecial values 29, 700 cal. at 298° A. Lewis and Randall give the fairly concordant value 28,910 cal., bit this was obtained very indirestly through the combination of results on a series of equilibria. Summary A study of the equilibrium of the reaction between ammonia and carbon, yielding as products hydrogen cyanide and hydrogen, has been described; and the free-onergy decrease attending the reaction at 8CO° A has been calculated. By the use of data on the ammonia dissociation and of heat data, the free energy of hydrogen cyanide gas has bean expressed as a function of temperature, and the special values ab 800° and 298° A have been given.