Example
Consider steam is undergoing a phase transition from liquid to vapor at a constant temperature of 20°C. Determine the entropy change sfg=sg-sf using the Gibbsian equations and compare the value to that read directly from the thermodynamic table.
From table A-4, T=20°C, P=0.002338 MPa, vf=0.001002(m3/kg), vg=57.79(m3/kg), uf=83.9(kJ/kg), ug=2402.9(kJ/kg)
sfg=(1/293)(2402.9-83.9)+(2.338/293)(57.79-0.001002)=8.375(kJ/kg K)
It compares favorably with the tabulated value sfg=8.3715(kJ/kg K)