Texts:
dp4 + sπ = HP
eq.1 in a closed system of constant composition, and no additional non-expansion work.
Step 1: Derive an expression for dπ using eq.1.
Divide both sides of eq.1 by dp4, and impose the constraint of constant composition.
Then, we obtain dπ/dp4 = (HP - sπ)/dp4.
eq.2
Step 2: Apply a Maxwell relation to eq.2.
Using a Maxwell relation of dπ/dp4 = (dHP/dV)T, we can rewrite eq.2 as:
(dHP/dV)T = (HP - sπ)/dp4.
So, we have successfully expressed dπ only with p, V, and T.