An engine using 1 mol of an ideal gas initially at 22.3 L and 266 K performs a cycle
consisting of four steps:
1) an isothermal expansion at 266 K from 22.3 L to 37.2 L
2) cooling at constant volume to 154 K
3) an isothermal compression to its original volume of 22.3 L
4) heating at constant volume to its original temperature of 266 K
Find its efficiency. Assume that the heat capacity is 21 J/K and the universal gas constant is 0.08206 L · atm/mol/K = 8.314 J/mol/K.