An ideal gas is heated so that it expands at constant pressure.The gas does work W.What heat is added to the gas?
A)W
B)-W
C)zero
D)more than W
E)less than W

Question

Quizplus · Accepted Answer

According to the first law of thermodynamics, the change in internal energy (ΔU) of an ideal gas is equal to the heat added (Q) minus the work done (W) by the gas. Mathematically,
ΔU = Q - W
Since the pressure is constant, the work done by the gas is given by
W = PΔV
where P is the constant pressure and ΔV is the change in volume. As the gas is expanding, ΔV is positive and hence W is positive as well. Therefore, in order for ΔU to be positive (which means the gas gains internal energy), Q must be greater than W. Hence, the answer is D, which says that more heat is added to the gas than the work done by the gas.

An Ideal Gas Is Heated So That It Expands at Constant