Why does changing the volume of a container change the pressure of the gas in it? Changing the volume reduces the number of molecules so they hit the walls of the container less often. Changing the volume reduces the force with which the molecules hit the walls of the container. Changing the volume increases the speed of the molecules so they hit the walls of the container more often. Changing the volume increases the area that the molecules collide with so the force is spread over a larger area.