The molecular theory states that the pressure exerted by a gas in closed vessel results from the gas molecules striking against the walls of the vessel. How will the pressure change if :

(a) the temperature is doubled keeping the volume constant

(b) the volume is made half of its original value keeping the temperature constant?

(a) This can be explained on the basis of Gas equation

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

When volume is constant we get,

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

Hence, when temperature is doubled, pressure is doubled, as pressure and temperature are directly proportional.

(b) This can be explained on the basis of Boyle's law

P₁V₁ = P₂V₂

Hence, when the volume is made half of its original value keeping the temperature constant, pressure becomes double, as pressure and volume are inversely proportional.