Thermodynamics--Gibbs free energy: what can we actually measure in the lab? Hi everyone: I am getting back into thermodynamics after a long absence and have realized that there are basics I have never understood. If a patient person could either explain or direct me to an online resource, I'd be very grateful. I have been on Google, but without success. Which thermodynamic potentials (U, A, H, G) can we actually measure directly in the lab (versus calculate)? I'm particularly interested in G. For example, if we consider the expression, G = H - TS, we can't measure entropy (right)? I know that Gibbs Free Energy of Formation values describe the amount of energy that is released or consumed when a phase is created from other phases. Does this mean heat energy? So we measure Gibbs Free Energy of Formation by measuring the amount of heat lost or given out by formation of a phase? How then do we separate out H and TS? Thank you very much.