State Gay-Lussac's law and illustrate the law with one chemical reaction.

Gay-Lussac's law of combining volumes

The law states that when gases react, they do so in volumes which bear a simple whole number ratio to one another and to the volumes of the gaseous products, provided the temperature and pressure remain constant.

Illustration with a chemical reaction

Consider the formation of ammonia:

N_2(g) + 3H_2(g) → 2NH_3(g)

Here 1 volume of nitrogen combines with 3 volumes of hydrogen to give 2 volumes of ammonia. The ratio 1 : 3 : 2 is a simple whole number ratio, which illustrates the law.

(The reaction H_2(g) + Cl_2(g) → 2HCl_(g), with ratio 1 : 1 : 2, is also acceptable.)