In other words, two water molecules or two moles of H two in a liquid state react to produce 1 mol of O, two in a gas state, and two moles of diatomic H, two in the gas state. Now let's look at a third type and a fourth type of chemical reactions, namely single and double displacement. Now, single displacement reactions are also known as substitution reactions. And double displacement reactions are also known as metaphosis reactions. So let's look at a single or substitution chemical reaction. So A plus B or AB plus C. What happens is that the bond between A and B is broken.