1. The problem statement, all variables and given/known data A closed vertical cylinder contains a mobile piston that splits it in two parts of volumes V1 and V2 with a ratio V1/V2=3. Both parts contain the same mass of an ideal gas at the same temperature T. Both chambers are heated to a temperature of 4T/3, find the ratio of the new volumes. Here's a little diagram to make it more clear. 3. The attempt at a solution Now i'm somehow confused because they don't specify if the mass of the piston is negligible. So, if the piston is in equilibrium and its mass is negligible then the resultant force that apply to the piston must be 0 => p1=p2, which is false because p1/p2=1/3. (where p=pressure) If the piston's mass is not negligible it has a mass m. p2=p1+mg/S p2'=p1'+mg/S (where g=gravitational constant, S=surface area of the piston) p2'-p1'=p2-p1 4nRT1/3 (1/V2' - 1/V1') = nRT1(1/V2-1/V1) 4/3 ( 1/V2' - 1/V1') = 1/V2 - 1/V1, from this i should conclude the V1'/V2' ratio but something might be wrong here, the problem statement is kind of misleading.