NOTES
2357
for the band. K e plan to report the results of such calculations for Pm+3 and for the other lanthanides in
in fused nitrates should be of considerable help in detecting small amounts of these elements in mixtures.
future coniniunications in this series. It is clear that the intensification of the band struc, Er+3 ture that is observed in Pm+3, nTd+3, H o + ~and
Acknowledgment. We wish to thank Dr. B. G. Wybourne for numerous helpful discussions and aid in carrying out the calculations.
NOTIES
Heat of Formation of (HOB0)3
by Jay A. Blauer and hlilton Farber Research and Deaelopment Laboratories, Maremont Corp., Pasadena, Califororrlia (Receiried FPhruary 24, 1964)
I n recent years there have been several attempts to give definitive values to the thermodynamic properties of (HOBOJ3(g). Based upon data obtained by means of mass spectrometry, Chupka, et u L , ~give a value of -540 i 10 k.cal./mole for its heat of forniatjon al' 298°K. This large uncertainty arises because about 99% of the volatile boron species in their apparatus was HOBO@, leaving only about 1% as (HOBO)3(g). Randall, et a1.,2 give -537.5 3 kcal./mole for the heat of formation of (HOB0)3(g)at 298°K. based upon transpiration experiments carried out at very high rates of flow (17 cm./min.). Whereas Randall, et u Z . , ~ were troubled with the need for making diffusion loss corrections, this was eliminated in the present study by employing a more suitable apparatus. The apparatus consisted of a Vycor tube with an 0.d. of 25 rnni. equipped with a capillary inlet (i.d. 2 mm.) and constricted to an i.d. of 17 nini. a t a distance of 12 mrn. from the inlet. A hollow Vycor plug having a central orifice of 2-mm. diameter was fitted tightly against the constriction and h d d in place by means of a solid quartz weight (see Fig. 1). The capillary inlet was wrapped with heating tape and kept a t a temperature in excess of 200". Nitrogen gas was passed through a heat exchanging coil immersed in a constant temperature bath and then through a fritted disk into distilled water, also heated by means of thle bath. The gaseous mixture was then passed through the transpiration cell, over liquid Bz03
which was contained in a platinum combustion boat. The amount of transpired nitrogen, and consequently of water vapor, was determined by collecting the nitrogen over water a t the end of the transpiration train. The rates of linear gaseous flow were in the neighborhood of 1 cm. per min. The combustion boat and its contents were weighed before and after each run. The runs were made a t varying gas flow rates. It was found that plots of (I'B,Ol/rEzO) us. rHpO, where I', represents the number of moles of species x which passes out of the cell per hour, were linear and could be easily extrapolated to zero flow by means of the method of least squares (see Fig. 2 and 3 ) . The values of the ratios (I'B,03/I'H10) were determined a t zero flow for each of the values of the water vapor pressure considered. The values are tabulated in Table I, the degrees of statistical freedom being taken
Table I : Extrapolated Transpiration Data T,
pH208
OK
atm.
1147 1147 1147 1147
0.704 0.308 0.488 0.132
0.0320 i 0,0023" 0.0203 i 0 . 0 0 1 5 0.02i9 1 0 . 0 0 1 7 0.0178i.0.0013
3 2 2 2
a w is the linear rate of gaseous flow. Degrees of statistical freedom. The uncertainties are the calculated standard deviations.
(1) W. A. Chupka, D. J. Meschi, and J. Berkowitz, J . Chem. Phys., 33, 530 (1960). (2) S. P. Randall and J. L. Margrave, J . Taorg. A V ~ ~Chem., ~Z. 16, 29 (1960).
Volzime 68, Number 8
A ~ i g i i s t 1964 ,
2358
KOTES
+ 0.5HzO(g) HOBO(g) 1.5&03(1) + 1.5H20(g) = (HOBO)3($) 0.5B,O3(I) + 1.5H,O(g) = H3B03(g) 0.5&03(1)
Figure 1.
Schematic drawing of transpiration cell.
=
(1) (2)
(3)
On the basis of these three reactions it can be shown that the following equation describes the condition holding a t equilibrium
(1.5K2 f O . ~ K P ) P H , O (4) where K1, K z Jand K 3 are the equilibrium constants for reactions 1, 2 , and 3 , respectively. The data are shown plotted in the form prescribed by eq. 4 in Fig. 4. 3.0
.. ..,
0
0
2
6
4 rH20
10
8
’
X 10’.
2.0
--
0
Figure 2. The effect of the rate of gaseous Bow upon the ext,ent of r e a d o n ; P = 0.308 atm.
X I&
..
ik
2.F: E
-2 0,
2 1.0
v
0
.-
L 0
I
0.2
0.4
0.6
I
0.8
I 1.0
P H ~ aOh, .
Figure 4. 0 1 0
I 2
rHlo x
4 10:.
Figure 3. The effect of the rate of gaseous flow upon the extent, of reaction; P = 0.704 atm.
as the quantity (n - 2 ) where n is the number of datum points corresponding to a particular water vapor pressure. I n the analysis of our experimental data it was assumed that each of the following reactions occurs The Journal of Physical Chemistry
The data plotted in the manner prescribed by eq. 4.
The data were treated by the method of least squares and the resulting values of the slope and intercept are tabulated in Table 11. On the basis of a Students’ t-test3 the value of the intercept does not differ significantly from zero; however, the value of the slope is highly significant and will allow further treatment. This indicates that within the pressure range considered in this study (3) A. Rald, “Statistical Theory with Engineering Applications,” John Wiley and Sons, Inc., New York, N. Y., 1957, p. 574.
NOTES
2359
--
Table I1 : Equilibrium D a t a
+
0.5K1
t ia
0 0031 i: 0 0026
1 19(-)
(l.6Kz 0.5Ka)
tab
0 0342 & 0 0095
3.62(++)
fC
7
a Students’ t-test for significance of intercept as compared to zero. Students’ t-test for significance of slope as compared to
’
zero.
Degrees of statiotical freedom
(ill ). 2
fi
- 2
tive ion. Appearance potentials of CF2+ from CF3X, X = F, C1, Br, and I, have been measured by Dibeler, Reese, and Nohler‘; and a separate set of these same measurements has been listed by Craggs and ?\4asseyJ2 mho also included CF2Clz. These two lists show considerable divergence and no consistent value for AH*(CF2+)can be deduced from those few cases for which the necessary auxiliary data are available. A direct electron impact measurement of the ionization potential of the CF2 radical has been reported by Reed and S n e d d e r ~who , ~ obtained a value of 13.3 e.v. We have now measured the appearance potential of CF2+ froin two new compounds, CF3H and CFzHz. These measurements lead to a consistent value for AHf (CFz+) and demonstrate that Reed and Snedden’s value for I(CF2) is too high. Appearance potentials were measured on a Consolidated Electrodynamics Corp. Model 21-103C mass spectrometer kindly made available by Harvard University. Ionization efficiency curves for the CF2+ ions were not parallel to that of the calibration curve (argon) and the appearance potentials were obtained by conventional extrapolation of linear plots. Results are given in Table I.
the monomer, HOBO(g), is only a minor product in comparison to the trimer, (HOB0)3(g). Thermodyna,mic function is for &B03(g)> HzO(g), and B203(l) have been tabulated by the Sational Bureau of S t a x l d a r d ~ . ~The . ~ entropy of (HOBO)o(g’) has been estimated by White, et al.‘~ On the basis of these tabulated functions the value of Ka a t 1147°K. is 0.0038 atm.””’. On the basis of this value and the value of the sltope of the line illustrated in Fig. 3, the value of K z is 0.0215 3t 0.0063 atrn.-”’. Employing the entropy listed by White, et CXZ.,~ the resulting heat of formation of (HOBO)a(g) a t 1147°K. is -544.8 0.6 kcal./mole. Interpolations within the heat capacity data tabulated for (HOB0)3(g)by White, et d,’? Table I 2.0 I.rcal./mole for the leads to a value of -545.8 heat of formation at 298°K. The uncertainty in thit; figure arises from the uncertainty in the heat capacity Compound data.
*
(4) Xational Bureau of Standards (E. S.),Circular 500, E. S.Government Printing Office, Washington, D. C., 195% ( 5 ) Sational Bureau of Standards (C. S.), Report 7093, TJ.S.Government Printing Office, Washington, D. C., 1960. ( 6 ) D. White, D. E.Mann, P.N. W’alsh, and A. Sommer, J . Chem. Phys., 32, 488 (1960).
Appearance Potentials of the Difluorornethylene Positive Ion
by W. C. Steelr: Depai tment of Chemistry, T u f t s University, Metiford, Massachusetts (Received February 84, 2984)
The continuing high level of interest in the chemistry of organic fluorine compounds has created a similar interest in the thermochemical properties of fluorocarbon radicals and ions. However, this area is characterized by a paucity of well established va,lues. This is particularly true of the difluoiromethylene posi-
CFsH CF2H2
Ap(CFn+), e.v.
A H i (CFa 9, koal. mole-’
1 4 . 7 & 0.4 14.8 i 0 . 4
240 =k 10 234 & 10
The heat of formation of the difluoromethylene positive ion has been calculated from the appearance potentials and known heats of formation of CF3H,4 CF*H2,4and HF,6 assuming the reactions
+ e CF2+ + HF + 2e CFz+ + Hz + 2e CF2Fr2 + e --+
CFsH
---j
The resulting values (Table I) agree to well within experimental uncertainty. Added support may be found from the appearance potential data of Dibeler, (1) V. H. Dibeler, R. M . Reese, and F. L. Mohler, J . Res. iVatZ. B u r . Std., 57, 113 (1956) (2) J. D. Craggs and H. W. S. Massey in “Handbuch der Physik,” S. Flogge, Ed., Vol. XXXVII/l, Springer-Verlag, Berlin, 1959, p. 314. (3) R. I. Reed and W. Snedden, Trans. Faraday Soc., 54, 301 (1958). (4) G. A. Neugebauer and J. L. Margrave, J . P h y s . Chem., 6 2 , 1043 (1968). (5) H. 31.Feder, W. N. Hubbard, S.S.Wise, and J. L. Margrave, ibid., 67, 1148 (1963).
Volume 68, Number 8
August, 1964
