When gases combine, they do so in volumes which bear a simple ratio to one another and to the volumes of the product if it is gaseous, provided all the volumes are measured at the same temperature and pressure.
N2 + 3H2 → 2NH3
1 vol 3 vol 2 vol
N2 : H2 : NH3 = 1 : 3 : 2
which is simple whole number ratio
Explanation of Gay Lussac's Law:- Consider a reaction
A + B → C + D
Suppose 'a' molecules of A react with 'b' molecules of gas B.
Let n molecules be present in 1 mL of gas A.
n molecules will be present in 1 mL of gas B.
Therefore, 'a' molecules will be present h a/n ml, of gas A
and 'b' molecules will be present in b/n mL of gas B.
The volume of reacting gases A and B are, therefore, in the ratio of a/n : b/n, that is, a : b which is the ratio of small whole numbers.
