Derive the thermodynamic identity for G (equation 5.23), and from it the three partial derivative relations 5.24.

Short Answer

Expert verified

The expression for change in G is (μdN-SdT+VdP) and the relations are

S=-GTP,N,V=GPT,Nandμ=GNT,P.

Step by step solution

01

Explanation

Write the expression for Gibbs free energy.

G=U-TS+PV

Here, G is Gibbs free energy, T is the absolute temperature, S is the entropy, P is the pressure and V is the volume.

Write the expression for the infinitesimal change in G.

dG=dU-TdS-SdT+PdV+VdP..(1)

Write the expression for the infinitesimal change in U.

dU=TdS-PdV+μdN

Substitute (TdS-PdV+μdN)for dU in expression (1).

dG=μdN-SdT+VdP..(2)

Rearrange expression (2) for constant P and constant N.

dG=-SdT

Rearrange the above expression.

S=-GTP,N
02

Calculation

Rearrange expression (2) for constant T and constant N.

dG=VdP

Rearrange the above expression.

V=GPT,N

Rearrange expression (2) for constant T and constant P.

dG=μdN

Rearrange the above expression.

μ=GNT,P

Thus, the expression for change in G is (μdN-SdT+VdP) and the relations are

S=-GTP,N,V=GPT,Nandμ=GNT,P.

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