Chemical reactions are described by chemical equations.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.we should balance the equation Because atoms are neither created nor destroyed in a chemical reaction, the total mass of products in a reaction must be the same as the total mass of the reactants.

The reaction between hydrogen and oxygen to form water is represented by the following equation.

2 H₂ + O₂---------> 2 H₂O

1 5 1