Everyone is familiar with phase transitions even it they are not familiar with the term. Amongst the most familiar is the melting of ice and the boiling of water to form steam. Technically, these transitions are called fusion and vaporization, respectively. There are more and we shall discuss some of them later.
All phase transitions are accompanied by changes in the free energy of the substance undergoing the transition, and this free energy has two components, the enthalpy of the transition and the entropy of the transition. Unless very careful work is being done, the entropy change is often ignored because it, in many cases, is the lesser contributor. However, it is never zero (except at absolute zero) and sometimes is the dominant factor.