Given the balanced equation representing a reaction:

4Al (s) + 3O2 (g) - - >2Al2O3 (s)

Which type of chemical reaction is represented by this equation?

(1) double replacement

(2) single replacement

(3) substitution

(4) synthesis

The answer is (4) synthesis. Synthesis reaction means that two or more reactants combine directly to one production. Substitution or single replacement means that one element of a compound is replaced by another element. Double replacement means that two ionic reactants exchange ions to form two new productions.