1. The problem statement, all variables and given/known data An engine works with an ideal diatomic gas (γ=1.40) according to a thermodynamic cycle consisting in four processes that take the gas successively through the states 1, 2, 3 and 4. The processes 1 -> 2 and 3 -> 4 take place at constant pressure and the two other processes are adiabatic. The cycle’s lowest pressure is 1 atm and corresponds to the state 1. a. Find an expression for the cycle’s efficiency exclusively in terms of the temperatures of the states 1, 2, 3 and 4. b. If the efficiency is φ=0.40, what is the gas pressure in state 3? 2. The attempt at a solution Ok, first part is easy (I guess) here's what I did http://imgur.com/hpBxIex if someone could give it a look I'd be very thankful. I'm sorry I cannot give you the P-V diagram because I don't know how to draw in this PC. The second part is where it gets tougher because I only have 2 pieces of information and I really cannot relate them. If someone could sketch the solution I'd be very thankful.