1. The problem statement, all variables and given/known data Two 800 cm^3 containers hold identical amounts of a monatomic gas at 20 C. Container A is rigid. Container B has a 100 cm^2 piston with a mass of 10 kg that can slide up and down vertically without friction. Both containers are placed on identical heaters and heated for equal amounts of time. What are the initial pressures in each container? 2. Relevant equations PV = nRT Q = nC*(delta)T W = - p*(delta)Volume 3. The attempt at a solution I've no idea. I've worked on this for 3 hours and I feel that I have two unknowns so far. I want to know the pressure in one of the containers, say V_1 for cylinder one. So... P = n*R*T/V_1 But how do I find the moles of this gas? And if that's not needed, what can I possibly do to fix this? I must be missing something obvious.