Example 2.3
The vapour pressures of a particular solid and of a liquid of the same material are given by ln p=0.04-6/T and ln p=0.03-4/T respectively, where p is given in atmosphere.
(a) Find the temperature and pressure of triple point of this material.
(b) Find the values of three heat of transformation at triple point. State approximation.

Solution:
At triple point the liquid pressure and solid pressure of the material coincides.

Temperature at critical point is 200 K.
Again,
For vaporization applying Clausius-Clapeyron’s equation

assuming ˜

(A)

Again vapour pressure of liquid material is given by

(B)

From A and B we get

Again, vapour pressure of solid material is ln p=0.04-6/T