A gas of temperature T₀ is enclosed in a container whose walls are (initially) at temperature T. Now, the gas exerts a higher pressure on the walls of the container when

The pressure of a gas is related to its temperature through the ideal gas law:

PV=nRT

If the gas has an initial temperature T₀ and the walls of the container are initially at temperature T, the gas will exchange heat with the walls of the container. If T is greater than T₀, heat will flow from the walls to the gas, causing the gas to increase its temperature.

As the gas's temperature increases, it will exert a higher pressure on the walls of the container.