Specific __________ does not change during a phase change (e.g. sublimation, melting, vaporisation etc.).

Correct Answer: Gibbs free energy

During phase change suppose consider liquid to vapor the entropy increases because randomness increases and the liquid converts to vapor by taking enthalpy so, enthalpy changes and generally the enthalpy of vapor will be greater than liquid.
We may think internal energy remains constant during phase change since temperature remains constant but here the potential energy changes thereby, changing internal energy since in vapor the distance between molecules is greater than the distance between the molecules in liquid hence the work made is different. So internal energy is different.
But we know Gibbs free energy is a function of pressure and temperature and during the phase change since pressure and temperature remains constant so, Gibbs free energy remains constant, but not zero.