One mole of water being in equilibrium with a negligible amount of its saturated vapour at a temperature `T_1` was completely converted into saturated vapour at a temperature `T_2`. Find the entropy increment of the system. The vapour is assumed to be an ideal gas, the specific volume of the liquid is negligible on comparsion with that of the vapour.

Explanation

The required entropy change can be calculated along a process in which the water is heated from `T_1` to `T_2` and then allowed to evaporate. The entropy change for this is
`Delta S = C_p 1n (T_2)/(T_1) + (q M)/(T_2)`
where `q` = specific latent heat of vaporization.