What is a major difference between a chemical reaction and a nuclear reaction?

 the major difference between a chemical reaction and nuclear reaction is that chemical reaction will result to only a change in the atomic number or simply the exchange of electrons trough ionic or covalent bonding etc.  While nuclear reaction involve change in the atomic mass, or simply number of nucleon in an atom.

Chemical reaction create compounds or molecules while nuclear reactions create atoms. Chemical reaction produce energy( heat, light) while nuclear reaction produce tremendous energy, to cause chemical reaction is relatively cheap  while nuclear reaction is difficult to accomplish. Nuclear reaction produce heap energy while chemical reaction produce expensive energy.