Entropy of fusion is defined as the entropy increase when a substance in solid state melts to liquid form. As there is a phase change, the entropy increases due to freeness of movement. It is equal to the enthalpy of fusion which is divided by fusion temperature. Fusion that occurs is associated with Gibbs free energy and has a negative value otherwise it is always positive. There is an exception; helium has negative fusion of entropy at temperatures lower than 0.3 K.