NOTES
Dec. 5, 1955
(Hs?&y 1380
(M) - CM (M)
- -c.4
(M)
....
PIYMYS 7 1
1
BlYYYS
0'7
.....
+0.0085 - .OS41
-
- ,0577
811-fMYan
0
. .. .. . ., . ...
0
... . ... .... .
yn nPnYMyafl
7"
1480
1330
+0.0108 ,0474
+0.0074
f0.0073 - ,0585
1.83 4.59
1370
1320
6197
+0.0107 - .0489
E
i
0
0
....
0
0
....
(MI - CM (M)
- _-Ca
(M)
( W 2
0
0
(M) - car P I ~ M " " ~ P,YMYSn (M) 71 . . . . 7, - __ CA 1 B I Y M ~ , nPnYMyan (M) (M) * '
7
81
+ PI (M) (MI - CM 1
(M) - -CA (M)
82
0
2P2
0
P1
82
1
(1L.I)
282
0
1210
+0.0135 - .0364
62.2
1160
+0.0136 ,0371
-
-0.0311 .2306
-
relatively large experimental errors because in the first case the determinant is always negative and in the second case i t is always positive. The method developed is also applicable to polynuclear species except t h a t the coefficients of the power series will contain (& explicitly I) in all coefficients corresponding to complex species which contain more than one
mayer, Rice and S t e p h e n ~ o n . ~In the present work the heat of solution of sodium borohydride has been measured and the heat of formation and entropy of the ion have been derived. Experimental
Sodium borohydride (Metal Hydrides, Inc., Beverly, Mass.) was purified by two successive recrystallizations from M2M (diethylene glycol dimethyl ether), the solution
NOTES
6198
by hydrolysis with HCI; three determinations gave values of 99.0, 99.6 and 99.8% of theoretical hydrogen. The calorimeter used was a new instrument to be described more fully a t a later date. It consists of a copper bomb of 700-ml. volume suspended in an evacuated submarine. Stirring is accomplished by rocking the assembly continually through BO", and the reaction is initiated by rotating it an additional 90' to unbalance a spring-loaded hammer which breaks the sample-bulb. Temperature changes are measured with a G-2 Mueller bridge and a calorimetric resistance thermometer to a precision of 0.0001'. Calibration is performed electrically, using a constantan heater, a regulated voltage power supply, a Rubicon Type B precision potentiometer, calibrated standard resistors and a relay operated from a standard clock. The bomb was loaded with 400 ml. of water and 5.00 ml. of 1.000 N NaOH to retard hydrolysis of the borohydride. In the third and fourth runs, the solution was degassed by repeated stirring and pumping through a vacuum line. Dissolution Reactions were initiated a t 25.00 f 0.03'. occurred very rapidly; the temperature change with the samples used was from 0.07 to 0.09'. The calorimeter was then cooled and calibrated electrically over approximateljthe same range.
Results
Vol. 77
the largest uncertainty being in the heat of formation of boric oxide. For the reaction 2, Stockmayer, Rice and Stephenson give the value AF& = -5660 f 70 cal. From this and the AHiga, one obtains ASFga = +16.4 f 0.3 e.u. Using the standard entropies of 24.26 for NaBH4(c)8and 14.4 for Na+,6 the entropy of borohydride ion is found to be 26.3 e.u., in good agreement with the value of 25.5 f 1 estimated by various means3 (8) H. L. Johnston and N. C. H d l e t t , T ~ r sJ O U R N A L , 7 6 , 1487 (1953).
RADIATIOX LABORATORY OF CALIPORSIA UNIVERSITY LIVERMORE, CALIFORNIA
On the Rate of the cis-trans Interconversion of Dichlorobis-(ethylenediamine)-cobalt(II1)Chloride BY DASIELT.HATVORTH, EDWARD F. SEUZIL ASD SCOTT L. KITTSLEY RECEIVED MAY10, 1 9 5
Four runs were performed as listed in Table I. TABLE I HEATOF SOLUTION OF NaBH4 -AH,
N,
Run
1 2 3
4
moles Ha0 moles NaBHk
cal. -
378 349 360 311
714 717 709 706
mole
Since i t is possible t h a t there might be some reaction of borohydride with dissolved oxygen, the last two runs will be weighted more heavily and we will write for the reaction XaBHa(c)
4-350HzO(e) = XaBH4.350Hz0 ( 1 ) AH = -709 5 5cal.
The cis-trans interconversion between the praseo and violeo complex was discovered by Jorgensen.' This note is concerned with the evaluation of certain kinetic data for the cis-truns interconversion of [C0(en)~Cl2]Cl.~ trans- [C0(en)~Cl2]Clwas prepared as described by Bailar.3 The green trans form is spontaneously converted into a violet cis form on standing in aqueous solution. The rate of conversion was followed with a Beckman D.U. spectrophotometer using 1.007,by weight (0.035 114) solutions of the trans form in all cases. It was found from a study of the spectrum of ths cis and trans forms that a wave length of GOO0 A. was suitable for following the rate of reaction. The temperature was controlled to f0.2". The rate constants were calculated froin the equation
The most probable systematic error would be due to the presence of a sodium borate; 0.5 weight 7; 2.303 T m - To Na~B407.5H20would make the above value 10 cal. k = -logt T m - Tt too positive. T o correct to infinite dilution, we where shall assume t h a t the heat of dilution is the same as k = rate constant that for NaBr given by Harned and Owen6 and T m = transmittance a t infinite time shall ignore the effect of the 0.0124 M NaOH in the TO = transmittance a t zero time solutions. Hence for the reaction Tt = transmittance a t time t
+
NaBHa(c) = N a + BHcAH& = -776 cal.
(2)
t
=
time in seconds
The rate constants a t various temperatures are listed in Table I.
Since the heats of dilution of NaBr and NaI dif'rAU1.E I fer by only 10 or 20 cal. over this range,6i t seems 'l'eml,., " C . f(.cc. ') probable t h a t this value is reliable within these lim"(i. 0 2 .iO X I O 5 its. 35.3 1 15 x 10 ' Applying a correction for the present best value 40.0 .i m x 1 0 - 4 for the heat of formation of HaB03. HzO, -257.32 50.0 L' 51 x 1 0 ~ kcal.,' the value of Davis, Mason and Stegeman2 for the heat of formation of NaBH4(c) becomes The energy of activation, A&, was found to be -46.15 kcal. Using -57.270 kcal. for the heat of 41.7 kcal./mole from a plot of log K us. 1/T. formation of Na+,6 the standard heat of formation OF CHEMISTRY of borohydride ion is calculated t o be +10.4 kcal., DEPARTMENT ( 5 ) H. S. Harned and B. B. Owen, "The Physical Chemistry of Electrolytic Solutions," Reinhold Publ. Corp., S e w York, N. Y..19% (6) F. D. Rossini, el a l . , "Selected Values of Chemical Thermodynamic Properties," Circular of t h e hTBS. No. 500, 195'2, (7) E. J. Prosen, "Thermochemistry of Boron Hydrides and Related Compounds," American Chemical Society, Cincinnati. 1955.
MARQUETTE UNIVERSITY 3, WISCONSIN MILWAUKEE
&I. Jorgensen, J. p v a k t . C h i n . , 3 9 , 18 (188!1); 41, 419 rlS!JO) (2) Ethylenediamine is designated as en. (3) J . C. Bailar, "Inorganic Syntheses." Vol. 11, ~ I c C r d w - H i l l Book Co., New York, N. Y., 1048, p. 223. (1) S.
