I've been having a lot of trouble in thermodynamics...are there any good sites that explain it? Here's my current problem: Would I need to use the equation of state to solve this problem? A cylinder contains oxygen at 20 degrees C, at a pressure of 15 atm and a volume of 12 L. The temperature is raised to 35 degrees C and the volume is reduced to 8.5L. What is the final pressure of the gas? Assume the gas is ideal. I've been trying to use PV = nRT (P is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is temperature in Kelvins). But that doesn't seem to be working out for me. But it would help to know if the number of moles varies based on the starting volume in liters or end volume in liters (using 1 mole = 22.4 liters). The only other equation that even makes sense to me is V = V[1 + beta (T - T) - k (P - P)]. But this is an ideal gas (well, you need to assume that it is) and you don't have beta or k to work with.