Find the pressure of saturated vapour as a function of temperature `p(tau)` if a temperature `T_0` its pressure equals `p_0`. Assume that : the specific latent heat of vaporization `q` is independent of `T`, the specific volume of liquid is negligible as compared to that of vapour, saturated vapour obeys the equation of state for an ideal gas. Investigate under what conditions these assumptions are permissible.

Explanation

From `C-C` equation
`(dp)/(dT) ~~ (q)/(T V'_2) = (Mq)/(RT^2) p`
Integrating `1n p = constant - (Mq)/(RT)`
So `p = p_0 exp [(Mq)/(R)((1)/(T_0) -(1)/(T))]`
This is reasonable for `|T - T_0|lt lt T_0`, and far below critical temperature.