One mole of an ideal gas expands isothermally at 300 K from 2.0 L to 6.0 L, absorbing 2740 J of heat. (a) Find the work done by the gas. (b) Find delta_U. (c) If the same expansion were done adiabatically with no heat exchange and the gas did 1800 J of work, what would delta_U be? Solution: (a) Isothermal ideal gas: delta_U = 0, so Q = W: W = 2740 J done by the gas. (b) delta_U = 0 - temperature unchanged. (c) Adiabatic: Q = 0, so delta_U = -W = -1800 J; the gas cools as its internal energy pays for the work.