The heat capacity at constant volume of hydrogen sulfide at low pressures is shown below, where T is in "C. C_{v}\left[\frac{k J}{m o l-K}\right]=0.0252+1.547 * 10^{-5} \cdot T A quantity

of H,S is kept in a piston-fitted cylinder with initial temperature, pressure, and volume equal to 25°C, 2.00 atm, and 3.00 liters, respectively. Why is there a difference between the energy required for a constant-volume versus a constant-pressure expansion?