1. The problem statement, all variables and given/known data A heat engine using 5.00 g of helium gas is initially at STP. The gas goes through the following closed cycle: - Isothermal compression until the volume is halved. - Isobaric expansion until the volume is restored to its initial value. - Isochoric cooling until the pressure is restored to its initial value. a)How much work does this engine do per cycle? b)What is its thermal efficiency? 2. Relevant equations thermal efficiency = Wout/QH (thermal efficiency)Carnot = 1 - TC/TH 3. The attempt at a solution for part a) I got: isothermal work = nRTln(V at 2/V at 1) = -1967 J isobaric work = p(V at 3 - V at 2) = 2836 J isochoric work = 0 total work done in one cycle = -1967 + 2836 = 869 J for pat b) i got: from 1 to 2: Q = -W = 1967 J from 2 to 3: Q = nC_p(deltaT), C_p for a monatomic gas is (5/2)R, this comes from the equipartition theorem Q = (1.25)(5R/2)(273K) = 7094 J from 3 to 1: Q must be negative since there is a work output so therefore Q in this process is irrelevant since we only need the Q that is added to the system efficiency = (total work done in one cycle)/(heat added in one cycle) efficiency = (869 J)/(7094 J + 1967 J) = 0.096=9.6% But apparently thats the wrong answer! I don't know what's wrong. Help!