NOTES
Jan., 1960
175
TABLE I INFRARED BANDSIN Pattern and sample
Amorphous 1. Freshly fused 2. Devitrified in air Hexagonal Hydrolysis in water a t 90-100" Dried a t 110' 3. Dried a t 400" Dried a t 1050' Hydrolysis, HC1 Ka4Ge9020 4. Commercial -4.D. Mackay Co. Commercial Eagle Picher Co. 5 . Hydrothermal 200" for 3 hr.
+
THE
SPECTRA OF GERMANIUM DIOXIDE
Indices of refraction NO NE
Bands ( p ) "
1.607 b
b
1.66-1.67 1.67-1.69 I .68-1.69
1.67-1.69 1.68-1.70 1.69-1.70
1.63-1.64
1.64-1.65
11,25b, s 11.40b, s
10.44W
2 . 9 5 ~6 . l w 6 . 5 ~7 . 0 ~7 . 6 ~10.22s 10.9sh 11.35b,s 6 . 5 ~6 . 9 ~7 . 5 ~10.43s 1 l . l s h 11.35b, s 6 . 5 ~6 . 9 ~7 . 5 ~10.43 11.05sh 11.35b; s 10.42s
11.44b, s
1.64-1. 66c
6 . 5 ~7 . 0 ~7 . 6 ~10.43s
11.25sh 11.47b, s
1.64-1.66~
6 . 5 ~7 . 0 ~7 . 6 ~10.42s 1l.Osh
1.697
1.724
10.44s
11.45b, s 11.45b, s
Tetragonal 6. Hydrothermal 400' for 3 days 1.9 2.1 12.9b, s 13.9b,S a sh-shoulder; s-strong; w-weak; b-broad. * Surface layer is hexagonal with same indices as hydrolysed variety. Very fine pou-der, treatment uncertain, probably hydrolysed from GeC14.
which rise as the reaction proceeds, as does the broad band of the spectra, until the characteristic rhombohedrons of the hexagonal form appear. The rhombohedrons have the appearance of forming only after solution and redeposition from solution, while the lower index material described above appears to be the result of an in situ type inversion. The cubical habit of the hexagonal form prepared hydrothermally is of interest since it displays diagonal extinction in contrast to that observed for the same habit by Laubengayer and Morton.6 The difference in indices of refraction of the products of the two preparations has been previously pointed 0ut.3'4 It is presumable that under hydrothermal conditions mater penetrates the amorphous structure and aids in the formation of centers where inversion takes place. The resulting crystallites are small and variably oriented so that under crossed nicols a rotating black cross is observed in the clear birefringent crystals rather than complete extinction. As shown by the loss of 0.9% weight and non-appearance of the weak broad bands near 3 and 6 p after drying the sample a t 400" absorbed water detectable by infrared methods has been removed. Ignition a t 1000" caused a total loss of weight of 1.3% but the indices were raised to only between 1.68-1.70 and the broad band of the spectra was not moved perceptibly from 11.35 p. The presence of other crystalline forms has been disproven by X-ray and the presence of a low index compound with water has been ruled out.' The extremely small and randomly oriented crystallites of the "hydrolysed form" could contribute to the low index of refraction of this form, whether prepared from the enneagermanate, tetrachloride or inverted from the amorphous form. The presence of the amorphous form as a minor part of a mixture does not appreciably affect the infrared
pattern of the hexagonal form other than in the possible formation of a shoulder on the broad band and also the presence of a small amount would not be detected by X-ray analysis. As only the products of the incomplete inversions to single crystals exhibit, in addition to the low index of refraction, an anomalous location of the broad band a t 11.35 p , it is presumable that the band location is varied by the presence of small centers of incompletely inverted glass. Thus, it is evident that to be reproducible, the infrared patterns of inorganic compounds prepared by inversion must be based on well crystallized samples.
THE COMPOSITIOK AND ENTHALPY O F DISSOCIATED WATER YAPOR BY P. J. FRIELA N D R. C. GOETZ Geiieial Electric Company, Missile and Space Vehicle Departmelit, Philadelphia 4* Pennsylvania Received J u l y 88, 1969
We have calculated the enthalpy arid composition of dissociated water vapor to 5000°K. for total pressures between 0.001 and 10 atmospheres assuming the gas mixture to be in chemical equilibrium. In this temperature range the following reactions occur
+
Hz0 = '/zH2 OH HzO = '/202 Hz '/zHz = H 1/20* = 0
+
(1)
(2) (3) (4)
The equilibrium constants for reactions 1 to 4 are
NOTES
176
Vol. 64
1.o 0.8 .e U
8 0.6
Where X is the mole fraction of the various species and pt is the total pressure of the gas mixture. There are six composition variables in the system. Therefore, in order to determine the gas composition a t any temperature and pressure (starting with one mole of undissociated water vapor) two additional equations are required in addition to the four shown above and they are
YI
c)
8 0.4 16' 0.2
0 10
0 Temp., OK. Fig. 1.-The composition of dissociated water vapor from 1600 to 5000°K.; total pressure 0.001 atm.
3000 4Ooo 5000 Temp., OK. Fig. 2.-The composition of dissociated water vapor from 1600 to 5000°K.; total pressure 0.01 atm. 1000
0.8 -
d
_-
2000
---
I -
r-7-1-77 -
1
1
---~ __
~
- -
- -
t:
__-
_ _ --ik IYXH
-
.2 0.6 0
t
r
+
-~
/
1
t--
7
C&=1
i.e., the sum of the mole fractions of all components must equal one and i.e., the hydrogen-oxygen ratio must always equal two. Values of the equilibrium constants in equations 5 to 8 at various temperatures are available in the Consequently, the composition of the gas can be determined at each temperature for various total pressures by solving equations 5 to 10simultaneously. This system of equations has been solved by an iterative technique on the Burroughs El01 Digital Computer. The results are shown in Figs. 1 to 5 in which the mole fraction of each component is plotted as a function of temperature for total pressures equal to 0.001, 0.01, 0.1, 1 and 10 atmospheres. Shown in Fig. 6 is a plot of 2, the total number of moles of gas formed by the dissociation of one mole of water vapor as a function of temperature for the various pressures. The enthalpy of the gas mixture was determined simply by calculating the energy required to form a gas of the various compositions shown in Fig. 1 to 5 a t room temperature (298.1'K.) and adding to this the energy required to heat a gas of this composition from room temperature to the temperature under consideration, i.e. H
1000
2000
3000
5000
4000
Temp., OK. Fig. 3.-The composition of dissociated water vapor from 1600 to 5000OK.; total pressure 0.1 atm. 1.0
0.8
-----
(9)
2.
=
+
A H ~ Q ~ n,(HiT i
- H,,,,)
(11)
where AH298is the heat of the reaction (1 - nH,o)HzO = no0
+~
E f H no,Oz
+ ~ H , H+z %OHOH (12)
and ni is the number of moles of i in the mixture (i = H20,0, H, etc.) HITis tBe enthalpy content of species i at temperature I' while Hizosis the enthalpy content of i at 298.1'K. Also
I
AHzm =
nlHfI
- (1 - %HrO)HfHtO
(13)
i#H10
where the first term refers to the heat of formation of the products of (12) at 298.1"K. (i = 0, H, etc.) o the heat of formation of water vapor. and H ~ H , is Values of the heats of formation of the various species at 298.1"K. and their enthalpy contents at 1000
2000
3000 4000 5000 Temp., O K . Fig. 4.-The composition of dissociated water vapor from 2000 to 5000OK.; total presswe 1 atm.
(1) V. N. Huff and C. S , Calvert, Nag. Advisory Comm. Aeronaut., Tech. Notes, 1653 (1948). (2) H. W. Wooley, ibid.. 3270 (1955). (3) V. N. Huff, 4t al., NULL Advisory Comm. Aeronaut., Rcpt.. 1037 (1951). (4) F. D. Rossini, 4t al., Natl. Bur. Standards (I?. S.), Ciro. 461, 1947.
A'OTES
Jan., 1960 1.o
li7
NON-ADDITIVE POLAROGRAPHIC WAVES I N THE ANODIC OXIDATION OF IODIDE
0.8
BY ALVINL. BEILBY'AND A. L. CRITTENDEN Department of Chemistry, University of Waehinoton, Seattle, Tashinoton Received Auurst 6 , 1969
al
20.4
w
Cases of failure of polarographic waves to be additive have been discussed by Miller and Orlemann2 and more recently by Anson and Lingane3 and g0.2 by A ~ e r b a c h . ~I n these cases, ope of the products of the electrode reaction diffuses from the electrode 0 and reacts with incoming reducible species to form 1000 2000 3000 4000 5000 a reducible species having a different diffusion coTemp., OK. efficient. Fig. 5.-The composition of dissociated water vapor from Kolthoff and Jordan6 have observed two waves 2000 to 5000°K.; total pressure 10 atm. in the anodic oxidation of iodide in chloride medium a t rotating platinum electrodes; the first corresponding to oxidation to iodine, the second to oxidation to iodine monochloride. The second step was found to be lower than the first step when .-b_ _._-_ the electrode was rotated but of equal height when the electrode was stationary. The explanation given was that iodine is formed very rapidly but - ~ _ - _- _ _ ~ that its subsequent oxidation to iodine chloride is slow enough to permit some iodine to escape from the electrode. A similar lowering of the second step was observed by Morgana at stationary electrodes. It appears that the lowering of the second -L ---+wave can be explained adequately, a t least for stationary electrodes, by the reaction of iodine chloride with incoming iodide to form slower-diffusing 1000 2000 3000 4000 6000 iodine. h numerical calculation of the magnitudes Temp., OK. of the two waves expected as a result of these ideas Fig. 6.-The total number of moles of gas (2)formed by the has been made. It has been assumed that, for the dissociation of water vapor. second step, both iodine and iodide are oxidized immediately to iodine monochloride a t the electrode and that the concentrations of iodine and GOO iodide are zero a t the electrode surface. It is assumed that the three species, together with chloride, are in equilibrium except a t the electrode sur500 face. The initial solution contains only iodide and chloride. It is further assumed that the concen400 tration of chloride is sufficiently large that its concentration may be regarded as constant through300 out. Linear diffusion is assumed.
' 7 r=
200 100
0 1000
Fig. 7.-The
3000 4000 5000 Temp., O K . enthapy of dissociated water vapor.
2000
various temperatures are also availahle.3-s The results of the enthalpy calculations are shown in Fig. 7 in which values of H/RTo ( R = gas constant, TO= 273.16"K.) are plotted as a function of temperature for various pressures. Values of H/RTo for constant values of 2 are also indicated. ( 5 ) F. D. Rossini, et al., ref. 4. Circ. 500,1952. (ti) J. Hilaenrath, et a l . , ref. 4, Circ. 564, 1955.
Experimental The electrical charge transferred during a fixed period of electrolysis from a fixed time ( h ) after application of cell potential to a second fixed time ( t t ) a t constant potential was measured using previously described equipment .7 The microelectrode was in the form of a square plate forged on the end of a platinum wire and sealed into the end of a vertically-mounted glass tube. Such an electrode should be more nearly planar than a cylindrical wire. Also it has been shown that diffusion to cylindrical electrodes is essentially linear under the conditions used .7 Measurements were made at 25.0'. ( 1 ) Based on the Ph.D. thesis of Alvin L. Beilby, 1958. Standard Oil Company of California Fellow. 1057-1958. (2) 8. L. Miller and E. F. Orlemann, J . A m . Chem. Soc., 7 6 , 2001 (1953). (3) F. C. Anaon and J. J. Lingane, ibid., 19, 1015 (1957). (4) C. Auerbach, A n a l . Chem., SO, 1723 (1958). (5) I. M. Kolthoff and J. Jordan, J. A m . Chem. Soc., 76, 1571 (1953). (6) E. Morgan, Thesis, University of Washington. 1956. (7) G. L. Booman, E. Morgan and A. L. Crittenden, J. Am. Chem. SOC.,18, 6533 (1956).
