Praxis II: Chemistry Exam Prep

Correct Response: A. The change in the system’s internal energy is equal to q (heat) + w (work). In this case Q is negative (–2.5 kJ) because the process is exothermic, and w is negative (–0.5 kJ) because the system does work on its surroundings. Therefore, the system’s internal energy is calculated as –2.5 kJ – 0.5 kJ. B is incorrect and is calculated as –2.5 kJ + 0.5 kJ. C is incorrect and is calculated as 2.5 kJ – 0.5 kJ. D is incorrect and is calculated as 2.5 kJ + 0.5 kJ.