The pressure will increase, because there is physically less space available for the same amount of gas. The volume of gas increases because the number of moles is increased. Mass and volume should remain constant. With the pressure and number of moles held constant in a sample of gas, turning off the burner and allowing the gas to cool will produce a constant ratio of volume to temperature. If the gas had a volume of 5.0 cubic meters, the temperature would be 375 degrees Kelvin.
Extensive properties depend on the amount of gas.
As the gas molecules collide with the walls of a container, the molecules impart momentum to the walls, producing a force that can be measured.