A chemical reaction is the process in which atoms present in the starting substances rearrange to give new chemical combinations present in the substances formed by the reaction. These starting substances of a chemical reaction are called the reactants, and the new substances that result are called the products.. When the reaction is between an acid (any compound that forms hydrogen ions) and a base (any compound that forms hydroxide ions), water is formed as one of the products. This is called neutralization. An example of a neutralization reaction is seen in the reaction above between sulfuric acid and sodium hydroxide.