1. The problem statement, all variables and given/known data The pV-diagram in Fig. P20.51 (See attached file) shows the cycle for a refrigerator operating on 0.850 mol of H2. Assume that the gas can be treated as ideal. Process ab is isothermal. Find the coefficient of performance of this refrigerator. 2. Relevant equations K = QC/|QH - QC| pV = nRT Cp = Cv + R Isothermal expansion: Q = W = ∫p dV = nRT*ln(V2/V1) Constant volume: Q = nCvΔT Constant pressure: Q = nCpΔT 3. The attempt at a solution QC = Qa-b + Qb-c = nRTa * ln(Vb/Va) + nCv(Tc - Tb) = paVa * ln(Vb/Va) + VbCv(pc - paVa/Vb) QH = Qc-a = n(Cv + R)(Ta - Tc) = pc(Cv + R)(Va - Vc)/R My answer K = QC/|QH - QC| = 0.462 Correct answer K = 6.23 What did I do wrong?