Change in Gibbs energy of ideal gas associated with pressure change
The total derivative of Gibbs energy under equilibrium conditions is written as follows:
The equation of state of an one-mole ideal gas, PV = RT, leads to change in Gibbs energy from pressure Pi to Pf:
where Vm is the molar volume.
Molar Gibbs energy of this ideal gas at a temperature T and standard pressure of P∅ is written by Gm∅ (T). Then, molar Gibbs energy Gm of this gas at this T and a given pressure of P is obtained as:
Namely, Gibbs energy of an ideal gas increases as a function of logarithmic pressure. Note that the symbol “∅” indicates that it is at standard pressure.