Excess - GCSE Chemistry Definition

In GCSE Chemistry, "excess" refers to when there is more of a reactant than is needed to completely react with the other reactant(s) in a chemical reaction. Imagine you are making sandwiches, and you have more bread than filling; the extra bread is in excess. In chemistry, when one reactant is in excess, it means that not all of it will be used up during the reaction, and some will be leftover. This helps identify the limiting reactant, enable calculations about the amount of product(s) formed, reduces waste by using the right amounts of chemicals, and improves safety by avoiding leftover hazardous substances, hence making chemical reactions more cost-effective and efficient.