A system has a heat source supplying heat to an ideal gas at a rate of 187.0 W and the gas is doing work at a rate of 130.9 W.At what rate is the internal (thermal)energy of the gas changing?
A) 56.1 W
B) 318 W
C) -56.1 W
D) 187 W

Question

Quizplus · Accepted Answer

The first law of thermodynamics states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. Therefore, the rate of change in internal energy is given by:

ΔU/Δt = Q - W

where ΔU/Δt is the rate of change in internal energy, Q is the rate of heat added to the system, and W is the rate of work done by the system. Plugging in the given values:

ΔU/Δt = 187.0 W - 130.9 W 
ΔU/Δt = 56.1 W

Therefore, the answer is A) 56.1 W.

A System Has a Heat Source Supplying Heat to an Ideal