What is the physical significance of Gibbs free energy. I mean I can't correlate it with practical world?
Gibbs free energy basically determines whether a reaction will be spontaneous (-ve) or non spontaneous (+ve). When a piece of sodium is dropped in water, it immediately reacts with water. Hence, the process is spontaneous, i.e. it does not require a catalyst to drive it forward, or anything to initiate it. In a non spontaneous reaction, a chemical reagent is required to force the reactants to react.