Consider NH3 vapor acting as a van der Waals gas with coefficients a = 4.169 atm-L2-mol-2 and b = 0.0371 L-mol-1. How much heat must be added to 50.0 g of the gas so that it experiences no change in internal energy as it undergoes isothermal reversible expansion from a volume of 1.00 L to a volume of 6.00 L at 298 K?