Consider a gas in a cylinder with a piston. When heat is supplied to gas, there will be work done by the gas on the piston-- gas expands. My question is: as the gas expands, why would there be a decrease in pressure of the gas as the volume increases and the piston moves up? I know because Boyle's law says so but can someone please give me an answer of what is exactly happening please? Because I thought as gas particles gain energy from heat, they move faster hence hit the piston harder (i.e. a greater force exerted on the piston). If soshouldn't gas pressure increase as volume increases due to P=F/A?