Zn is suffering a loss of electrons, hence it is getting oxidized. Its oxidation number is changing from 0 to 2. In the same equation, the hydrogen is reduced. If everything is counted through the entire equation, oxidation and reduction are equal and balance to 0. Isomers occur mostly in organic chemistry.
Example below shows one example of isomerisation reaction.
Even though ammonium cyanate and urea have the same chemical formula, their arrangements of atoms inside the molecules differ. They have different structures and hence widely differing physical and chemical properties. There are few other reactions which need mentioning. These again can be subdivided into precipitation and neutralization reactions. In a double displacement reaction, two substances react by exchanging their radicals and form two completely different compounds.