Question

A certain liquid has a vapor pressure of 92.0 Torr at 23.0 °C and 313.0 Torr at 45.0 °C. Calculate the value of ΔH°vap for this liquid.

Answer 1

Given Data :

P 1=92 torr
P 2=313
T 1=296 k
T 2=318
Hvap = 47900 Joules
R=1.99 cal/mole-k

Using Clausius-Clapeyron equation :
logP2/P1 = delta H/(2.303*R) * (1/T1-1/T2)

log 313/92=0.53
2.303*R= 2.303*1.99
= 4.5829 cal/mole-k
1/T1-1/T2=1/296 - 1/318
= 0.0000233
delta H = 0.53*4.5829/0.000233
delta H = 10424.622 cal