A gaseous reaction takes place inside a frictionless piston–cylinder apparatus at constant external pressure. During the reaction the surroundings perform 40kJ of compression work on the system (w=+40kJ for the system). Simultaneously, the system releases 150kJ of heat to a surrounding water bath.
Answer the questions below regarding the energy changes for this process.
(1) Calculate the change in internal energy ΔE for the system and state its sign.
(2) Classify the reaction as endothermic or exothermic. Support your classification by referencing both q and ΔE.
(3) Explain, in terms of the first law of thermodynamics, how the values of q and w you used in part (a) together account for the overall energy change of the system.
(4) If the same reaction were instead carried out at constant pressure with a negligible change in volume, discuss qualitatively how the numerical values of q, w, and ΔH would compare to those in the original experiment.