A system is acted on by its surroundings in such a way that it receives 50 J of heat while simultaneously doing 70 J of work.What is its net change in internal energy?
A) 70 J
B) −20 J
C) zero
D) 20 J

Question

Quizplus · Accepted Answer

According to the first law of thermodynamics, the change in internal energy (ΔU) of a system is equal to the heat (Q) added to the system minus the work (W) done by the system: ΔU = Q - W. In this case, ΔU = 50 J - 70 J = -20 J. The negative sign indicates that the internal energy of the system has decreased. Therefore, the best choice is B.

A System Is Acted on by Its Surroundings in Such