2. An ideal gas initially at 298 K and a pressure of 5 atm is expanded to a final pressure of 1 atm (a) Isothermally and reversibly, (b) isothermally against a constant pressure of 1 atm, (c) adiabatically and reversibly, Solution Isothermal: An isothermal process is a change of a system, in which the temperature remains constant: ?T = 0. Adiabatic: an adiabatic process is one that occurs without transfer of heat or matter between a thermodynamic system and its surroundings. Reversible: reversible process is a process whose direction can be \"reversed\" by inducing infinitesimal changes to some property of the system via its surroundings, with no increase in entropy. In our case ideal gas is allowed to expand at constant temperature, hence it is isothermal. As pressure is reduced to normal pressure the change is not reversible change. Thus option a and C are not our answers! The pressure is going to be constant 1 atm throughout change hence answer is option b) isothermally against a constant pressure of 1 atm. .