If 30 kJ of heat flows out of a system and 15 kJ of work is done by the system,then what is the change in internal energy?
A) 85 kJ
B) 70 kJ
C) 45 kJ
D) 15 kJ
E) 10 kJ

Question

Quizplus · Accepted Answer

According to the first law of thermodynamics, the change in internal energy (ΔU) of a system is equal to the amount of heat (Q) added to the system minus the amount of work (W) done by the system:

ΔU = Q - W

In this case, Q = -30 kJ (since heat flows out of the system) and W = 15 kJ, so:

ΔU = -30 kJ - 15 kJ = -45 kJ

Therefore, the change in internal energy of the system is -45 kJ. However, the question asks for the absolute value of the change in internal energy, so the answer is 45 kJ (choice C).

If 30 KJ of Heat Flows Out of a System