Calculate the volume (in cm³) of air expelled from a vessel containing 0.4 litres of it at 250 K, when it is heated to 27°C at the same pressure.

1 lit = 1000 cm³
∴ 0.4 lit = 400 cm³

V₁ = Initial volume of the gas = 400 cm³
T₁ = Initial temperature of the gas = 250 K
T₂ = Final temperature of the gas = 27°C = 27 + 273 = 300 K
V₂ = Final volume of the gas = ?

By Charles' Law:

$\dfrac{\text{V}$1}{\text{T}1} = \dfrac{\text{V}2}{\text{T}2}

Substituting the values :

$\dfrac{400}{250} = \dfrac{\text{V}$2}{300} \\[1em] \text{V}2 = \dfrac{400 \times 300}{250} \\[1em] \text{V}_2 = 480 \text{ cm}^3

Volume of air expelled = 480 - 400 = 80 cm³