Dec., 1963
HE:ATSO F
SOLUTIOX O F
HYDROGEK CHLORIDE AND HYDROGES BROMIDE IS TVCTTER
2521
HEATS OF SOLUTION OF GASEOUS HYDROGEN CHLORIDE AKD HYDROGEN BROMIDE IN M'ATER AT %iol BY CECILE. VANDERZEE AND JAMES D. NUTTER~ Avery Laboratory of Chemistry of the University of Nebraska, Lincoln, Nebraska Received August 19, 196s By direct calorimetry, the standard heats of solution ( A H , " ) of gaseous HC1 and HBr in water a t 25" were found to be -17,875 and -20,350 cal./mole, respectively, with a standard deviation of 1 7 cal./mole. operate close to the expected final temperature in the calorimeter Introduction in order t o avoid evaporation effects in the calorimeter and t o The discrepancy between the calorimetric standard provide small temperature drifts in the after-period. In this heat of solution of HCl(g) and that obtainable from way a long after-period could be recorded without change of bridge dial settings and more accuracy attained in evaluating e.m.f. and entropy data appears to be resolved by the the final reaction temperature. In the after-periods, the sensi, ~ rerecent calorimetric nork of Gunn and G r e e i ~ who deg./mm. of recorder chart; fore-periods tivity was 1 X ported AHSO = -17,888 caI./moIe a t 25'. Data deg./mm. Reactions were initiated a t were run a t 2 X taken from e.m.f. studies with the Ag-AgCI e l e ~ t r o d e , ~ - ~25.00", and electrical energy equivalents were run on the final together with entropies of Ag and AgCl(s) from Cirstate of the system. All heats are reported in terms of the thermochemical calorie, defined equal to 4.1840 absolute joules. cular 500,7lead to A H S O = -17.89 i 0.03 kcal./mole. Several techniques for bringing the gases into the calorimeter These values are in reasonable agreement with the were tested and modified. The most satisfactory device for gases early work of Wrewsky and Savaritsky.8 The value which dissolve completely and rapidly was constructed from a 20selected in 1952 for Circular X07 (- 17.96 kcal./mole) em. length of 2-mm. capillary tubing, the upper end of which extended through a chimney in the calorimeter lid and was attached appears to be weighted in favor of the work of Roth and Richter.g Later work by Roth and Bertram'O leads t)o with a T joint close to a 3-way stopcock on the gas storage line. The lower end was sealed to a hemispherical bell (diameter 4 em., values ranging from - 17.88 to - 17.75 kcal./mole. volume ca. 16 ml.), which was immersed to the juncture of the The data of Roth, et aLJg even when corrected to 25" bell and capillary. The total volume of the capillary and conand infinite dilution, show a disturbing trend with connecting joint was about 2 ml. At the beginning of the reaction period, the 3-way stopcock was opened and the gas delivered into centration as well as considerable scatter. the calorimeter liquid a t a constant rate (1 ml./sec.) by a motorEven more disturbing trends are found in the data of driven Hg piston in a gas buret. At this rate of delivery, the Roth and Bertramio for the heat of solution of HBr(g). small amount of initial air ( 2 ml.) in the delivery bell served as a Corrected to 25' and infinite dilution, their heats of diluent and control on the rate of solution of the gas.'& In visua1 solution fall from --20.36 kcal./mole a t 0.22 m to tests, the gas dissolved smoothly with no tendency to escape from the bell. Two minutes after the flow of gas was stopped, the gas -118.50 kcal./mole at 0.001 m, the greatest change ocwas almost back to original size. At this point 4 ml. of bubble curring below 0.04 m. The data of Thomsenll support air was introduced slowly through the 3-way stopcock to sweep a value between -20.34 and -20.45 kcal./mole. Cirthe last traces of HC1 or HBr gas out of the capillary into the solucular 5Q07gives -20.24 kcal./mole. It appears that tion. Three minutes later, the stopcock was opened to the atmosphere, and three 1-ml. pulses of calorimeter solution were drawn uncertainty in the standard heat of solution of HBr(g) is up into the bell and capillary as a rinsing procedure to wash down even worse than existed for HCl(g). any traces of concentrated acid solution in the lower end of the I n this paper we present results of calorimetric meascapillary. This washing procedure normally yielded only small urements in which we first confirmed the results of amounts of heat (ea. 0.3 cal.). A 'blank' rinsing procedure was Gunn and Green3 by a quite different technique and carried out after completion of the run to establish a correction for 'noncheniical' heat transfer associated with the rinsing procethen used the same procedure in determining AH,"for dure. HBr(g). Since heats of dilution of HBr were available The gas introduction technique meets the following requirefrom a separate study in this LaboratoryJi2it seemed ments: (1)uniform conditions exist in the calorimeter in the final advisable to standardize the heat-of-solution procedures state; (2) there is no escape of HCl or HBr in the form of fog a t around a single concentration and set of conditions, any point in the calorimeter, and no loss of water vapor; (3) heat rather than to work with widely varying amounts of is evolved a t a uniform rate, permitting more reliable evaluation of the "corrected temperature rise." material as did Roth, et aLgl o
Experimental Calorimetric Apparatus and Techniques .-The design and operation of the solution calorimeter has been described elsewhere.:3>l4 The thermostat, controlled t o f0.001", was set to (1) From the Ph.D. thesis of James D. Nutter, November, 1963. (2) Monsanto Chemical Co Fellow, Summer, 1963. (3) S.R. Gunn and L. G. Green, J . Chem. Eng. Data, 8 , 180 (1963). (4) R. G. Bates and V. E. Bower, J . Res. +Watt.Bur. Std., 63,283 (1954). (6) H. S.Harned and T. R,Paxton, J . Phys. Chem., 67, 531 (1953). (6) J. G. Aston and F. L. Gittler, J. A m . Chem. SOC.,77, 3173 (1955). (7) F. D. Rossini, D. D. Wagman, W.H. Evans, 8. Levine, and I. Jaffe, "Selected Values of Chemical Thermodynamic Properties," National Bureau of Standards Circular 500, 1952. (8) M. Wrewsky and N. Savaritsky, 2. phyazlo. Chem., 112, 90 (1924). (9) W. A. Roth and H. Richter, ibzd., 8170, 123 (1934). (10) W. A. Roth and A. Bertram, 2. Elektrochem., 43, 376 (1937). (11) J. Thomsen, "Thermochemische Untersuchungen," Barth, Leipzig, 1882-1886; ref. 10 quotes Thomsen's data. (12) C. E. Vanderese, J. D. Nutter, W. W. Rodenburg, and &I.L. Rodenburg, unpublished work.
The temperature of the incoming gas was that of the thermostat; the resulting correction amounted to no more than 2 cal./ mole, and was computed for each run. Preparation of HCl(g) and HBr(g).-The gas storage buret and associated lines were evacuated for several hours prior to introduction of gas, and tested for leaks. During storage, the gases were held a few millimeters above atmospheric pressure. A fresh sample of gas was prepared for each run. Gaseous HC1 was prepared by dropping concentrated A.R. grade sulfuric acid onto A.R. grade sodium chloride in an evacuated generator flask. The gas was passed through a cold trap
(13) C. E. Vanderzee and R. A. Myers, J . Phys. Chem., 65, 153 (lQ61). (14) (a) C. E. Vanderzee and J. A. Swanson, zbid., 67, 285 (1963); (b) {bid., 67, 2608 (1963). (15) It was found essential to keep the volume of initial air this small. With larger amounts (e.@.,5 ml. or more), or when 0.5% or more of insoluble gas was present in the HC1 (HBr), equilibration was slow, and fog formation in the vapor space was frequently observed. Under these conditions transfer of heat and material could not be simultaneous, and resulting data had much less precision, together nith large systematic error.
2522
('ECIL
~CSI~ERIMEKTAI,
13. VAXDERZEE ASD JAMES D. NUTTEI~
DATAFOR
n t . 1120,
3Ioles IIX,
Concn ,
6.
nx
m
THE
1029.4 1037.9 1029.2 1046.2 1037,i 1025.6 1038.2 1037.5 1036.7 1012.4 1045.6 1015.8
0.023666 .023322 ,023207 .023739 ,023875 .023435 ,023375 ,024018 ,033620 .023338 ,023505 .023610
0.022990 .022470 .022549 .022691 I023008 .0222550 022515 ,023150
1040.8 1035.3 1036.5 1037, !I 1034,2 1032.2 1039.3 1037.6
0.023519 .022305 .022653 ,022464 .021406 .022573 .0?1715 .022500
0.022597 .021544 .021655 ,021644 ,020698 .021869 020894 .021685
.022i81
.vi3052 .022810 .032576
Vol. 67
TABLE I HEATSOF SOLUTIONOF HCl(g) A N D IiUr(g) I N H20 AT 25' AOxs
Be/%,
oc.
cal./deg.
HCW 0.37141 .36478 .36455 .368i5 .37385 ,37003 .36567 .376oG .37024 .37413 .37124 .36712
Qx,
cal.
1133.6 1137.7 1132.9 1145.8 1137.0 1128.1 1137.5 1136.6 1135.0 1110.2 1142.1 1145.3
421.02 414.99 412.99 422. ri3 425.05 417.44 415.94 427.44 420.43 415.34 423. 98 420.48
177!)0 17794 1779G 17799 17803 17813 17793, 17797 17800 17797 17811 17809
17865 17869 17871 17874 17878 17888 17869 17872 17875 17872 17886 17x84 Mean 17875
1139.8 1134.2 1139.9 1136.8 1137.8 1135.2 1138.1 1136.4
476.81 452.18 459.14 455.21 434.06 457.62 440.51 456.06
20273 20273 20268 20264 20277 20273 20286 20269
20350 20350 20345 20341 20354 20330 20363 20346 Mean 20350
HBrW 0.41833 .39867 .40278
.40044 ,38148 .40313 .38705 .40130
(-78") to rcinovc condensable irnpurities and then into the gas btorage system. Gascous HBr from a cylinder (Matheson) \vi19 condensed in a cold trap (liquid nitrogen) and melted. The first fraction was puiripcti off and diwxrded; then a venter fraction was distilled into the gas storage line. Al)out one-third of the material reinained in the trap and was discwded. The sainplcs of Ill3r were prepared within 20 rnin. of their use in a. calorimetric run. During this interval there was no signifivant attack upon the Hg in the gas dclivery buret. Analyses.-All solutions were prepared and analyzed on a mold t ~ s i s and , all weighings were correrted to vacuum. The distilled wtiter, collcc+xI above 85", \+as stored in scmoned containers with precautions against absorption of COZ. I n most cases the specihc resistanres of the water were above 1 X lo6 ohm. cm. Eac*h b:
