A nuclear reaction is a reaction which brings change in the nucleus of an atom.
For example,
A chemical reaction is a reaction which results in the formation of new compounds which have different properties than their reactants.
Hence, in a nuclear reaction changes in an atom occurs whereas in a chemical reaction changes in a compound or molecule occurs.
Thus, we can conclude that a major difference between a chemical reaction and a nuclear reaction is that only nuclear reactions can change the identity of the atom.
Freezing: Liquid turns into solid. Evaporation: Liquid turns into gas. Condensation: Gas turns into liquid. Sublimation: solid into gas. Deposition: Gas into solid.