Hi, this is my first post on here. My question relates to adiabatic cooling/heating of a gas. I am trying to grasp the idea conceptually rather than being able to explain it mathematically per se.... When gas escapes rapidly from a pressurised cylinder the rapid expansion of the gas is facilitated by the heat energy within the gas, causing its temperature to fall (as there has been no time for the transfer of heat energy from the surrounding environment). However, the First Gas Law states; P1/V1 = P2/V2 @ constant temperature. There has been in increase in the volume of the gas but there has also been a reduction in the pressure of the gas. Would not the potential energy of the high pressure of the gas (when in the cylinder) be enough to account for the increased volume of the gas at greater volume (once escaped from the cylinder)? Or, if you were to look at it in terms of the ideal gas equation; PV = nRT, I would expect that as the volume increased, the pressure would decrease in accordance with this and the temperature would remain constant. I don't understand why the 'system' needs the addition of energy (taken from the heat energy of the gas in the case of an adiabatic process).