Considering the equation :
iron + sulfur heat -----> iron sulfide
or
Fe + S -----> (heat) FeS
So, When iron and sulfur react to form iron sulfide. The chemical composition in the reactants that is of iron and sulfur is different from the chemical composition of the products that is iron sulfide. But in a physical change, the chemical composition of the sample doesn't change. So this reaction is a example of chemical change.
