I'm having some trouble with a question involving a piston pressing down on an enclosed gas. I'm given the height of the cylinder, the number of moles of gas, the mass of the piston, and told that initially the gas is at STP. I need to find the height of the piston when the system is in equilibrium. I thought I knew how to do it, using PV = nRT. I calculated the area of the piston at (about) 1 square meter, so I decided the pressure pushing up should be about the piston's mass * acceleration due to gravity, correct? Since the mass of the piston is only 1.4 kg, I get about 14 Pa as the necessary pressure. But this is only an extremely small fraction of the original pressure of 1 atm, so the height difference seems negligible to me. Am I missing something, or am I going to be giving my answer in millimeters?