In: Chemistry
The heat of fusion of ice is 80 cal/g at 0 °C and 1 atm, and the ratio of the specific volume of
water to that of ice is 1.000:1.091. The saturated vapor pressure and the heat of vaporization of
water at 0 °C are 6.026 × 10-3 atm and 600 cal/g, respectively. Estimate the triple point of water
using these data
Clausius-Clapeyron Equation:
For vapouration curve: lnPv = -Hv/RT +K1
Sublimation curve: lnPs = -Hs/RT +K2
At triple point: Vapour pressure of solid = Vapour pressure of liquid = Vapour pressure of gas
At triple point, sublimation curve and vapourisation intersects
-Hv/RT +K1 = -Hs/RT +K2
(Here T is the temperature of triple point)
Hs = Hv + Hf = 80 + 600 = 680 cal/g
We need to find out values of constant K1 and K2
lnPv = -Hv/RT +K1
ln0.006026 = -600 / 2 x 273 +K1
K1 = -5.11 + 600 / 2 x 273
K1 = - 4.01
lnPs = -Hs/RT +K2
ln1 = 680/2 x 273 +K2
0-680/2 x 273 = 680/2 x 273
K2 = -1.245
-Hv/RT +K1 = -Hs/RT +K2
-600/T- 4.01 =- 680/T -1.245
T = 28.9K