stirring blades on the end, but also had a hole near the bottom which perniitted bubbling inert gas through the solution in the c,iloriitieter. The water in the calorimeter was deaerated before each run. Three runs gave for AII, -9..'37, -9.46 arid -9.31 kcal./rnole. With the aid of the Debye--Huckel equation, these heats were extrapolated to infinite dilution to give --!I~M, - 0 . 7 2 anti --9.+-)7 kcal./ iiiole. We shd1 take 111' = - - ( I ( 1 4 4- 0.10 kc,il./mole for reaction i L J. By adding together the heats for reactions ( l ) , f-?), ( 3 ) and (41, wcobtnin for ( 5 ) , ATI' = -25.1 2.0 kcal./mole. I3y atltlirig AII' = - 1 0 kcal./ iiiolec for reaction ((ij, we ol)lniii AI! - --2O.l + 2.0 kcnl. 'mole for reactioii ( Y ) . 'Thr. two experinientally iiitlepentlent methods have givcn essentially the S:LIIIC value for the heat of reaction ( 7 ) , :mrl wr 5h'ill t,ikc AI€" = -26.0 r 1 .O k ~ a l . , ' ~ i ~ ~ l r . I'ugh, Laubengayer and Jlorton,? Schwarz 10) N,itionnl nurenu uf Standard\ i t . l t ( r c d V ? l i l t s o f Clivtmrnl 'l%ermoriynannc Properties, Wabhington, D C 11147 el "q (7) \I' I'iij!~ J C/iz?ri 5uc l i ? ; (!ViY!) ( % A !V I i i i l x ~ l l ~ i ~i iei rrl I ) > \?ortoii T I ~ I~So l I K N 4 I 64, 2715
and Huf9 and Winkler"' measured thc solubility of GeOz a t various temperatures. From the temperature coefficient of the solubility, we can obtain an approximate value for the heat of solution of the soluble form of GeOz. It appears that the two low temperature measurements of Schwarz and Huf give solubilities which are too high. For the process €IzO GeOp(ppt.) = H2Ge03(nyjwe cdculate 111' = +2.2 i 1.0 kcal./mole. Pugh gave the solubility of GeOp in water as 4.4T g. per liter a t 25', while Laubengayer and Morton reported 4.53 g. Taking an average of 4.30 g. per liter, we find AFO = +1.80 kcal./mole for the solution of C>e02. Combining this with the above heat yields A S o = f.t.7 k 3.1 e.u. By estimating Sa = 1:3 e.u. for G e 0 2 (using Latimer's tables") we calculate the cntropy of F12Ge03(ac1)to be 34.3 i-4.0 e.u. For the oxidation of GeT2to GeOz by triiodide
+
21120
-t GeI?(s)
we calculate AIIO
+ It-
= GeOJ(s)
= - 29.3 &
+ 4T-I- + ,?I-
1.4 kcal./mole.
(9) R Schwari arid R H i i f . Z. nnovg Chem , 203, 1 0 - 1 11'471) (10) C Winkler, J p r a l l Chein , [ Z ] 34, 2 1 1 (1880) (11) tV hI L,itimer TI115 I U I J R U ~73, I , 1480 (1'1711
(ill??)
[COXTRIBUTION FROM 'TIE DBP.4RTMRST
RADIATIOU LABORATORY,
O F CHEMISTRY AND CIIEMICAI. ENGINEERING, AND T;NIVERSITY O F CALIFORNIA
1
The Vapor Pressure of Germanic Iodide. The Entropies of Germanic Halides. The Disproportionation of Germanous Iodide RY WILLIAIIL. JOLLY^ AND WENDELL 31. LATIMER RECEIVED JULY 7, 1932 Germanic iodide sublimes readily a t temperatures in the neighborhood of loo", and in this research the vapor pressure has been measured over a range of 55'. These data have been employed t o calculate AF" and A H D for the sublimation. Since there are no values for the entropy of GeIl(g), the method of Hildebrand has been employed t o estimate the vibrational frequencies and hence calculate the entropy. The vapor pressure of GeI,(g) over mixtures of Ge and GeI2 has been measured over a range of 100". These data have been employed to calculate AF' and A H o for the disproportionation of GeI?.
The Vapor Pressure of Ge14(s).-A saturated vapor flow-method was employed. Germanic iodide crystals were placed in a horizontal glass tube which was heated to a constant temperature while n steady stream of argon was passed through the tube. By assuming that the gas was saturated with GeIr vapor in passing through the tube, the amount of GeI4 which condensecl out on the cooler portions of the tubing was taken as n nit'asure of the vapor pressure. I
Experimental Procedure.-Germanic iodide was prepared by the method of Foster and Williston.2 The product w a ~ purified by r e c r p l l i z a t i o n frnrn chloroform followed by air drying at 80 . Two methods for heating the tube containing the GeId were used. I n two low temperature experiments the tubing was heated by a vapor-jacket similar to that used in Abderhalden driers. The vapors of boiling benzene and of boiling water were used to maintain the temperatures 79.8 and 99.8', respectively. Higher temperatures were maintained by heating the tubing in a horizontal tube furnace. A "Celectray" electronic controller (C. J. Tagliabue Mfg. (1) Taken from a thesis presented by William L. Jolly for partial satisfaction of the requirements of the P h . D . degree, University of
California. 1962. i Z ) L. S . Poster ~ n r lA. 1'. WilliPtoo. I m r ~ S. y n l l m s ~ s 9 . , 112 (1040).
Co.) was u\ed in conjunction with a chromel-alumel thermocouple t o keep the temperature of the furnace constant to kt.7". The thermocouple was calibrated at the boiling point of water and the melting points of ice, tin and cadmium. A sheath of nickel foil was wrapped around the tubing where the GeIl was contained. Linde argon was freed of oxygen and water by passing the gac consecutively through hot copper turnings arid magneiium perchlorate. The total volume of gas passed in a ruii was determined by collecting the gas over water a t the end of the flow system. ( I t wai necessary to correct for the vapor pressure of water ) The runs were timed with a n TABLE
I
VAPORPRESSURE OF GeId(s) Total ~. .~.
Run T , OK.
Time, min.
Flow rate, mole A/min.
1OR 0.74F X 206 0.387 X c 393 47 1.69 x 10-3 0 (extrap.) 393 D 408 75 0.527 X lo-* E 379 203 .774 x 10-8 I' 873.0 215 ,735 x 1 0 - 3
A
99.7
I3 393
c;
3&?.0
3uo
,634
x
10.'
pressure in tube, Calcd. vapor presatm. snre of GeIi, a t m .
0.999 1.007 1.008 1.010 1.000 1.002 O.OQQ
8 . 2 x 10-4 8 . 4 X lo-' 7 . 1 x 10-4 8 . 7 x 10-4 1.79 X 2 . 9 x 10-4 2.20 x io-' 4.7
x lo-'
----
VAPORPRESSURE OF GERMANIC IODIDE
Nov. 20, l9.‘2
electric timer; runs were started by suddenly bringing the temperature up to the desired point and ended by suddenly removing the heat. Quantitative condensation of the volatilized Ge14 was found to occur in the cool, narrow tubing immediately outside the hot zone. This narrow tubing was cracked off after each run and the sublimed GeI, was dissolved. The iodide was titrated to IC12- with a standard permanganate solution. Details of the run are given in Table I. Runs A, B and C were carried out a t the same temperature, but with different flow rates. I t can be seen that relatively good vapor saturation is attained if the flow rate is kept below about 0.7 x 10-3 mole argon/minute. The error due to incomplete saturation in the remaining runs is probably less than 10% in the vapor pressure. Interpretation of Data.-A very satisfactory representation of vapor pressure data is given by an equation of the form A F o = AH: - AC; T I n T f I T where AH: and I are empirical constants. In this case AC,” is the difference in heat capacity between the gas and solid. In the second part of this paper we calculate C,? = 25.1 for GeId(g) a t 25’; by Kopp’s rule we estimate C,? = 33 for the solid. Taking AC,O to be -8, we have plotted AC,” In T , ‘L‘CTSUS 1 / T . the “sigma function,” A F ” / T The slope of the straight line drawn through the points is AH; = 22,500 cal./mole. The intercept on the 1 / T = 0 axis is I = -90.8. Hence the free energy of sublimation of GeI4 can be represented within experimental error by the equation A F o = 22,500 f 8 T In T - 90.8T The heat and entropy of Sublimation can similarly be represented by AHo = 22,500 - 8T A S ” = 82.8 - 8 In T At 298’K., these functions have the values: AF& = 9.0 kcal./mole, AH& = 20.1 kcal./mole, AS& = 37 e.u.
+
800
(3) For GeFc: P . J. H. Woltz and A. H. Nielsen, J. Chem. P h y t . , 20, 307 (1952).
(4) For GeClr: J. T. Neu and W. D. Gwinn, THIS JOURNAL, 70, 3403 (1918). ( 5 ) For GeBrr: G. Herzberg. “Infra-Red and Raman Spectra of Polyatomic Molecules.” D. Van Nostrand Co., Inc., New York, N. Y.. 1945. (G) For GeFr: A. D. Caunt, H . Mackle and L. E. Sutton, Trans. Faraday SOL, 47, 943 (1951). (7) For GeClr: L. Pauling and L. 0. Brockwag, TAXS JOURNAL, 67,
2684 (1935). (8) For GeBrc: M. W. Lister and L. E. Sutton, Trans. F a r n d n r 87,393 (1941) and M . Rouault, A n n . phys., 14,78 (1940). ( 0 ) I. H. Hildebrand. J , C h r n . Phrr., 16, 727 (10471,
Soc.,
I
it ) d
I
700
-
600
1.
8- 500
b %
QJ
2 400
LI
B
*
.C
-;;;300 200
100
0
1.6
The Heat Capacities and Entropies of Germanium Tetrahalides.-Sufficient experimental data exist for germanium tetrafluoride, germanium tetrachloride and germanium tetrabromide to calculate their entropies on the basis of molecular constants. Both the vibrational energies3+ and the interatomic distancese-8 are known. It was necessary to estimate the vibration frequencies for GeL. Hildebrandg has shown t h a t when v1 and v2 (for various tetrahalides) are plotted against interatomic distance, smooth curves are obtained, which are roughly straight lines. The points on each curve are characterized by the same halogen and mode of vibration; each point on a given curve represents a tetrahalide with a different central atom. An extension of this idea was used in estimating the frequencies for germanium tetraiodide. Figure 1 shows a plot of all four vibrational frequencies of GeF4, Gee14 and GeBr4 against the GeX distance. It is apparent that the points for a given mode of vibration form a smooth curve, approximating a straight line. (A similar set of curves is obtained for the silicon tetrahalides.)
a ‘
I
t>
1.8
Fig. 1.-Vibration
2.0
2.2
2.4
2.6
Ge-X distance, A. frequency for germanium tetrahalides.
Lister and SuttonE give 2.50 A. for the Ge-I distance in germanium tetraiodide; by extrapolation we find v1 = 116 i 1.5, vz = 30 f 10, v3 = 238 20, v4 = 62 f 10 em.-’. Using tables of Einstein functions1° and the standard thermodynamic equations, the heat capacities a t constant pressure and standard entropies of the germanium tetrahalides were calculated. The results are shown in Table 11.
*
TABLE I1 HEATCAPACITIES A N D ENTROPIES OF GeX,(g) AT 29833°K. C,”,
GeF4 GeCl, GeBr4 GeI4
so I
cal./deg. mole
cal./deg. mole
19.57 22.97 24.34 25.1
72.51 83.05 94.77 107.9
The Disproportionation of Germanous 1odide.Brewer and have observed that when germanous iodide is heated, it decomposes into germanic iodide and germanium metal. In this investigation, the vapor pressure of GeIr(g) over mixtures of Ge(s) and GeIz(s) was measured over the temperature range 544-643°K. (10) H. L. Johnston, L. Savedoff and J. Belzer, “Contributions to the Thermodynamic Functions by a Planck-Einstein Oscillator in One Degree of Freedom,” Office of Naval Research, July, 1949. (11) F. M. Brewer, J . Phys. Chcm., 81, 1817 (1927). (13) F. M. Brewer and I.. M. Dennis,ibid., 91, 1657 (1927).
Experimental Procedure and Results.---The preparation of germanous iodide has been dewribed in another publication by the authors.l3 A Sdtut2tCd vapor flow incthud, \iit11 ail apparatus siiiiilar to that for nieasuring the vapor pressure of solid &I4 was used. (.;el2 crystals i r e r e placed in a glass tube through which dry argon was passed. The tube \vas hcatcd by a tube furriacc (saiiic method of control as in the GeId vapor pressure experiments) and the volurne of gas passed through the tube was measured b y collecting it over triter. When the tube W ~ heated S t o about 270" reaction cotnmenced and cloud? of GeII dust began emerging from the furnace. Some of the Gera (approximately 50%) condensed in the cool, narrow tubing leading from the reaction chamber, but the reniaiiider passed right into the container used for collecting the argon a t the end of the line. -4tlditional coiled glass tubing was put into the line beyond the furiiace in an attempt t o condense out the OeI,, but even with more than a meter of tubing for condensation, some of the GeId particles were swept through the line. Thus it was impossible t o accurately determine the amount of GeI4 formed by collecting t h a t which condensed out i n the cooler tubing. However, two runs were carried out using this method; the results are given in Table 111. In these two runs, the condensed GeId was dissolved out of t h e tubing and titrated with permanganate. I n addition t o GeI, being evolved due to the disproportionation of GeI?, some GeI? sublimed a n d quantitatively condensed out. At the end of the runs, this GeI? could be easily separated from the condensed GeI4, because the GeI? coritfensed out i n a much hotter zone (almost within t h r furnace) than did the Ge14. This sublitnet1 Gel: \vas also dissolved and titrated with permanganate. Thus these rneasuremepts yielded both the vapor pressurr of (;?I,, ;tiit1 t h r pressure of Ge14 dne to disproportionntioii.
TABLE rri VAPORPRESSURES OVER G e
+ GeI:
Pressure of Geld, atm
Run
T , '1;.
C'
,557
4.1
x
D'
.I;),
$ 3 . ii
>
