Two 800\; cm^3 containers hold identical amounts of a monatomic gas at 20^\circ 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. Suppose the heaters have 25 W of power and are turned on for 15 s. What is the final volume of container B? I found the initial pressures of both container B, I then plugged that into the initial pV=nRT to find n, then plugged that into E=[nc(constant pressure)deltaT] using 25x15=375 J as the value for E. This determined delta T, I then plugged that (with T = delta T + 293) into the final pV=nRT to get V. This seems like it's probably too complicated, and I didn't get the right answer...can someone please help??