To discover whether an unknown gas is monatomic or diatomic, an experimenter takes a 2.0 L sample of the gas at STP and heats this sample to 100C at constant volume. (a) The gas absorbs 180 J of heat-energy in this process. Is this gas monatomic or diatomic? (b) The experimenter weighs the sample and finds it has a mass of 2.5 g. What molecule or atom comprises the gas? (c) The experimenter then releases a piston and allows the gas to cool to room temperature 20C under constant pressure. How much work does the gas do (take care of the sign)?