Find the change in internal energy of the gas during each of the four steps.

The PV diagram shown is for a heat engine that uses 1.000 mol of a diatomic ideal gas as its working substance. In the constant-temperature processes A and C, the gas is in contact with reservoirs at temperatures 373 K and 273 K, respectively. In constantvolume process B, the gas temperature decreases as heat flows into the cold reservoir. In constant-volume process D, the gas temperature increases as heat flows from the hot reservoir.