Entropy for Solids and Liquids

Recall the Gibbs equation: Tds = du + Pdv .

This equation can be rearranged into the form:

Solids and Liquids can be estimated as incompressible as their volume does not change significantly under a process. therefore dv can be assumed to equal 0.

The equation then becomes:

as du = cdT,the equation then becomes:

If we integrate both sides between 2 states(state 1 and 2):

we get:

where c is the average specific heat across the 2 states:

is an appropriate estimate.