Gay-Lussac’s Law

Gay-Lussac studied mixtures of gases that would react under suitable conditions. The results of the study led to Gay-Lussac’s law of combining the volume of gases.

Gay-Lussac’s law states that when gases react, they do so in volumes that bear a simple ratio to one another and to the volumes of the products, if gaseous, provided that the temperature and pressure remain constant.

nuV (P, T constant)

It shows that the ratio between the combining volume of gases and the products can be expressed in small whole numbers.

For example;

\( \scriptsize \underset {2 \:vols}{2H_{2(g)}} \; + \; \underset {1\: vol}{O_{2(g)}} \; \rightarrow \; \underset {2 \:vols} {2H_2 O{(g)}}\)

In the equation above, 2 volumes of hydrogen combine with 1 volume of oxygen to give 2 volumes of steam.

Example 4.2.1:

Calculate the volume of oxygen required to burn 500 cm³ of methane completely.

Equation of reaction:
2CH_4(g) + 3O_2(g) → 2CO_2(g) + 2H₂O_(g)

Solution:

By Gay-Lussac’s Law,