Chapter 8, Problem 8.35NP

Interpretation Introduction

Interpretation:

The value of the ratio ∂P/∂T for the phase transition involving the vaporization of water needs to be calculated with and without the assumption that the molar volume of gas is much greater than that of the liquid.

Concept Introduction:

The relationship between pressure (P), temperature (T) and the enthalpy change (ΔH) associated with a phase transition reaction is given via the Clapeyron equation:

  $\left(\frac{\partial \text{P}}{\partial \text{T}}\right)\text{ = }\frac{\text{ΔH}}{\text{TΔV}}\text{ -----(1)}$

Here, ΔH and ΔV are the molar enthalpy and volume between the two phases and T is the temperature of phase transition

For a reaction at equilibrium, the free energy change ΔG = 0, therefore based on the thermodynamic equation

  $\begin{array}{l}\text{dG = VdP }-\text{ SdT}\\ \left(\frac{\partial \text{P}}{\partial \text{T}}\right)=\frac{\text{ΔS}}{\text{ΔV}}\text{ -----(2)}\end{array}$