Compléter Constant PressureVersion en ligne This explores expansion of a gas at constant pressure. par Larisa Gray 1 When a gas is heated the average energy of the particles increases resulting in an increased so the particles hit the sides harder and more often resulting in higher . If the on the outside is kept constant the piston will move increasing the . This reduces the of the particles so they don't hit the walls so often . The , therefore , falls until it is the same as before . This describes Law .