When a solid substance changes into its liquid state at its melting point, the process takes place by absorption of heat from the surroundings. e.g., melting of ice H2O(s)⟶‌H2O(l) ‌∆H‌fus ‌0=+6.0‌kJ‌mol−1 Thus, enthalpy change for this process is positive or there is an increase in enthalpy, but still the reaction is spontaneous, because the liquid state of water is more random than its solid state. Hence, it may be concluded that melting of ice is accompanied by an increase of entropy. ∆G=∆H−T∆S To sum up, a reaction to be spontaneous, the value of ∆G, i.e., the Gibbs' free energy change must be negative or there must be a decrease in free energy, thus, ∆H must be smaller than T∆S.