WENDELL M. LATIMER, PHILIPW.
SS
values obtained for the heat of solution of silver nitrate, mercuric cyanide, lead bromide and lead nitrate. These are all salts of metals that have a marked tendency to form stable complexes with ammonia. The heat effects in the case of the lead salts are particularly high. The value of 20,100 for lead iodide is close to that found by Kraus and Ridderhof for lead bromide, 29,600 cal.
Summary Some improvements to the liquid ammonia calorimeter of Kraus and Ridderhof are described. The heats of solution of silver nitrate, mercuric cyanide, lead iodide, lead nitrate, sodium chlorate and sodium bromide have been determined. PROVIDENCE, R I
RECEIVED S E P T F M n r R l t i , 1934
[CONTRTIII~TIOXFROM THE CHEMICAL LARORATORV O F THE I:SIVERSITY
O F CALlFORNIA]
The Heat Capacity and Entropy of Potassium Chlorate from 13 to 300'K. Entropy of Chlorate Ion
The
BY WENDELL M. LATIMER, PHILIPW. SCHUTZ AND J. F . G. HICKS,JR. This determination of the entropy of potassium chlorate completes the data on the entropy of the halogenate' ions. Material.--Potassium chlorate of c. P. quality was recrystallized from distilled water three times and dried at 110' for sixty-five hours. The s:tmple showed only very slight traces of chloride with acid silver nitrate. We are inTABLE I HEAT CAPACITYOF POTASSIUM CHLORATE MOLECULAR WEIGHTOF KC103 = 122.55 T,
O K .
Molal C p
1S . 95 1F ' . 84 1F.. 48 22.3.5 24. A n 2;. 79 3 2 , Fil 3 ; . 31 41. Iti 44.78
0.44
41..92 .5:i . 30 55,. 11 0:. 28
8.52 9.41 10.28
ii; $11 -r I
1
ti0
71.04 7r. (17 84.51 8C 32 94 8fi 10c. 26 10:. 92 111 69 117.17
(1)
0 77 1.28 2.01 2 ii2 3 53 4. f\7 5.84
A . 80 7 .iK5
11.13 11.82 12.x 12 59 13 lt5 13.77 11 23 14.68 15.06 l j .49 1R.9n 16.22
T ,OK. 122.64 128.23 133.91 139. 75 145. 79 161.83 157.89 164.on 169.83 175.89 181,35 182,23 189.02 19(i,71 204 38 212 30 220.76 229.13 23(i 81 24,5. 50 254.21 262.95 272.28 283.8.5 293.35
Molal C p
16.53 16.81 17.13 17.43 17. 75 18.07 18.37 18.65 18.89 19.20 19.40 19.46 19.89 20.18 20.51 20.79 21.12 21.47 21.84 22.04 22.57 22.84 23.33 23.39 23.84
(a) R a i R r O l ) ? , H ~ OGreensfelder . a n d Latimer, THISJ O U R N A L , 60, 32Rfi (1928); (h) AgIOa, G. and I,., { b i d , 63, 3813 (1931): ( c ) KBrOj a n d K I C h Ahlherg and 1-atimer, i b i d , to be published.
debted to Dr. J. E. Ahlberg for the preparation of the sample. Specific heat measurements were made on a sample weighing 1 lS.867 g. in V ~ C U O(0.0699 mole). Measurements.-The molal heat capacity values fall on a smooth curve and are presented in Table I and graphically as a function of log T in Fig. 1. The heating intervals employed in various temperature regions are as follows : below 30°K., about 3" per run; 30 to 200"K., about 5" per run and above 2OOoK., about S o per run. Entropy of Potassium Chlorate.-The entropy of KCIOa was obtained by graphical integration of the equation S:98
=
Lzg8
C, d In T from a
larger scale plot of the curve shown in Fig. 1. The curve was extrapolated graphically to 10°K. and by means of the T 3law below that. A summary of the entropy calculation is given in Table 11. TABLE I1 0-10"K T1 extrapolation 0 E54 F I' 10-298 1 ° K . Graphical 34 I l i i 15. IT.
S o at 298 1' of KClO,
=
.3 ' 4 17 I:
I-
The relative accuracy of 33.17 E. U. is estimated a t *0.05 per cent. Heat and Free Energy of Solution.-Stackelberg2 gives 10,500 cal. for AII" at 16' for the reaction KC103(s) = (K'
+ C103-) (hypothetical one molal)
Correcting this figure to 2 . 5 O qives SI.& 10,120 cal. (2) Stackelberg, Z p k y s / k Chem , 26, 540 (189x1
=
Jan., l!lX
HEATCAPACITY AND ENTROPY
$9
OF POTASSIrJM CHI,OR.\TE
clo+ ~ H+; The activity coefficient of potassium chlorate ' / a cl?+ ' 1 2 o2 -t ' 1 2 H2 AII = - i ~ 1 , 1 1 ) 0 7 cni. in a saturated solution a t 25" (0.715 has A S = -76.58 been taken as 0.476 because of the close agreement between the activity of potassium nitrate From these data we calculate the free energy of and potassium chlorate solutions4 below 0.1 m. formation of chlorate ion a t unit activity to be Experimental activity coefficients of potassium +3700 cal. From earlier data Lewis and Randall5 chlorate are not available 2j up to saturation. However, 0.476 cannot be far from the 20 true value. 'The free energy - . ..- . .. .- ... change involved in the trans1,5 fer of one mole of solid PO- 8 tassium chlorate to the aque10 ous ions a t unit activity is -1363.8 log (0.476 X 0.71f1)~ 5 = 1277 cal. as compared with the older value of 1570." 1.0 1.25 1.50 1.75 2.00 2.25 2.;iO Entropy of Chlorate Ion.-Log T . Substituting G I o = 10,120 Fig. 1.-Molal heat capacity of KClOs. cal. and 3.F" = 1277 in the expression for the first and second laws, we have find -250 cal. However, it is quite possible for the entropy of solution, = 29.7 E. U. that the error in the AII term is as large as this discrepancy. = SK+ ScIo3- - SK~lor. For the entropy of K + we shall use 24.6 E. U.6 We then obtain, Summary employing this value and Our entropy for PotasThe heat capacity of potassium chlorate has been sium chlorate a t 298.1°K, %lo3- = 39.3 12. u. measured from 13 to 300°K. and the curve of C, Free Energy of Chhrate Ion--For the re- us. log T integrated graphically. The entropy a t action 298.1' of thesalt has beenevaluatedat 34.1T E. U. (3) Seidell, "Scslubilities," D. van Kostrand Co., Xew York, The entropy of c103-has been calculated to be 1919, p. 512. 39'3 E' and the free energy Of formation '3700 (4) Landolt-Bornstein, "Tabellen," I1 Erganzungsband, p. 1122. ( 5 ) Lewis a n d Randall, "Thermodynamics and the Free Energy of cal., both a t 25".
+
'"
Chemical Substances," McGraw-Hill Book Co., Inc., New York. 1923, p. 511.
BERKELEY, CAL.
(6) T h e details of this calculation will be published shortly by Latimer, Schutz arid Hicks i n a complete revision of t h e ionic entropy values.
(7) "International Critical Tables," Vol. V, (8) S?o98.1 used are I/? CI? = 2 6 . 7 , a/! 09 = il 5 , C103- = 39.3, H + = 0
RECEIVED SEPTEMBER 21, 193.3 I/?
I I ? = 15.6.
