I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
September, 1946
LITERATURE CITED
Baeyer, A., Ber., 5, 1094-1100 (1S72). '2) Bailes, E. L., J . Chem. Education, 22, 122 (1945). '3) Breckenridge, J. R., Can. Chem. Process Ind., 28, 570-3 (1944;. (4) Callahan, J. .I.,Chem. &. M e t . Eng., 51 ( l o ) , 109-14 (1944). '5) Campbell. G. d.,and Vest. T. F.,Chem. Trade J., 115, 196-6 lj
(1944). 6) Darling, S. F., J . Chem. Education, 22, 170 ( 1 9 4 4 .
(7) Flei.k, E. E.. and Haller, H. L., IND.ENG.CHmi., 38, 177-8 (1946).
' 8 ) Fleck, E. E., and Preston. 11. K., Soap Sunit. ChemicaZs, 21, 111-13 (1945). 19) Frankforter, G. E., and Kritchevsky, W., J . A m Chem. .%e., 36, 151 1-29 (1914). . I O ) Glinther. F. .A,. Ihid.. 67, 189-90 (19453.
923
(11) Gunther, F. A , , J . Chem. Education, 22, 2 3 8 4 2 (1945). (12) Haller, H. L., et al., J . A m . Chem. SOC.,67, 1691-1602 (1945). (13) Iris, R. C., and Leyra, R. D.. Rea. inst. s a l u b r k h d enfermedadea t r o p . (Jlex.), 5, 74 (1944). (14) Katz, A., J . prakt. Chem., [2] 90, 311 (1914). (15) Jlueller, P. (to J. R. Geigy A-G.), U.S.Patent 2,329,074 (Sept. 7, 1943). (16) Rueggeberg, W. H., and Torrans. D. J., IND.ESG. CEEM.,38, 211-14 (1948). (17) Sumerford, TV. T.. J . Am. Pharm. Assoc., 34, 259 (1945). (18) Thorpe, E., "Dictionary of Applied Chemistry", Vol. 2 , pp. 180-1, New York, Longmans, Green & Co., Inc., 1921. (19) U. S. Dept. of Commerce, Office of Publication Board. Rep(. 360, 5 (1900). 20' Zeidler. 0 . .Ber.. 7, 1180-1 (1874).
Change of Latent Heat of Vaporization with Temperature T w o new rules for change of latent heat of vaporization with temperatures are presented, and their derivations given. It is believed that the new rules have the advantages of simplicity and general applicability to all liquids.
S
EVERAL investigators have reported results on the change of latent heat of vaporization with temperature (1,2 , 6 , 7-
f2). This paper presents some new rules for calculating the change of latent heat of vaporization with temperature. The new rules are simple and seem to have general applicability to all liquids. For vapor-liquid equilibria, the C,lapeyron equation is
dP
n
L
=
T(1.,
- Vf)
i
li
whrw
p = vapor pressure of a given liquid at temperature
T ( O K.)
from International Critical Tubics (3)except the duta on w,ter, which were taken from the steam tables of Iieenan and lieyes (4). The individual lines are surprisingly linear, but the slopcp are fairly different from 'one another; that is, at equal r e d u c d temperatures the reduced vapor pressures of various liquids are, in general, far from being equal to one another. The compressibility factor I.( changes with pressure as well as with temperature and was shown t o be a function of T and e (6) The ratio, T , of liquid volume to vapor volume p"r unit mass p l u y an important role only near the critical point for, a t low or moderate pressures, r is small and (1 7 ) is nearly equal to 1. The data arc correlated as the ratio of two latent heats of vaporization at any t x o temperatures. The reduced temperature and pressure are used as temperature and pressure measures. If r e assume a reference temperature eo at this f ~ ~ r n p r ~ ~ t i i r c Equation 1 becomes, for the same liquid,
-
Lo =
sa PO
R(1
- To)
(3)
Dil iding Equation 1 by Equation 3,
L = latent heat of vaporization per mole Vsr 1;
rf
=
molal volumes of saturated vapor and liquid. respectively
4)
If the vitpor pressure CUIY
