1. The problem statement, all variables and given/known data A heat engine uses the closed cycle shown in the diagram below. (Figure 1) The working substance is n moles of monatomic ideal gas. Find the efficiency of such a cycle. Use the values for pressure and volume shown in the diagram, and assume that the process between points 1 and 3 is isothermal. 2. Relevant equations pV=nRT efficiency = Wout/QH 3. The attempt at a solution We know that T3 and T1 are on an isotherm, and so are both exactly 3 times T2. So, the absolute value of ΔT is 2 times T2. The reason I refer to the absolute value here is because the sign of ΔT for different processes will be different. Wout = nRT*ln(V1/V3) - pΔV So, Wout = nRT*ln(V1/V3) - nRΔT QH= nRT*ln(V1/V3) + nCvΔT So the efficiency is: 3nRT2*ln(V1/V3) + 2nRT2 / 3nRT2*ln(V1/V3) + 2nCVT2 Then the idea is to cancel out all the n's and T2's. All the rest are knowns. I get a value of 84.1%. There's definitely something very wrong about my approach.