Clapeyron Equation
The Clapeyron equation, derived from the Maxwell relations, is used to determine the enthalpy change associated with a phase change.
Firstly, we'll have to recall the third Maxwell Relation:
During a phase change process occurring on a P-T diagram, the phase change occurs on the saturation pressure. The saturation pressure only depends on the saturation temperature and nothing else. Thus the partial derivative δP/δΤ is constant. It’s like finding the gradient using a tangent:
Given that the process above is occurring at a constant pressure and referring back to Gibbs:
