Praxis II: Chemistry Exam Prep

Category - General Chemistry

A system undergoes an exothermic process releasing 2.5 kJ of heat. During this process, the system does 0.5 kJ of work. According to the first law of thermodynamics, what is the change in the system's internal energy?
  1. –3.0 kJ
  2. –2.0 kJ
  3. 2.0 kJ
  4. 3.0 kJ
Explanation
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.
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