A mixture of 5L of H2 and 3L O2 reacts to form H2O (g) at constant T and P .Find the volume of H2O gas obtained. 2H2 (g) + O2(g)
2H2O(g)

The  volume of H₂O = 5 L

Given

5L of H₂ and 3L O₂

Reaction

2H₂ (g) + O₂(g)  ⇒2H₂O(g)

Required

The  volume of H₂O

Solution

Avogadro's hypothesis:  

In the same T,P and V, the gas contains the same number of molecules  

So the ratio of gas volume will be equal to the ratio of gas moles  

mol H₂ = 5, mol O₂ = 3

From equation, mol ratio H₂ : O₂ = 2 : 1, so :

mol H₂O based on mol H₂, and from equation mol ratio H₂ : H₂O=2 : 2, so mol H₂O = 5 mol and the volume also 5 L