Exemplar Problems

Problem 10 : A gas is compressed at constant temperature, and 500 J of work is done on the gas. Calculate the change in internal energy (∆U) for the gas.

Solution :

The change in internal energy (∆U) is related to the heat (q) and work (W) done on or by the system by the first law of thermodynamics:

∆U = q - W

In this case, 500 J of work is done on the gas, so W = 500 J.

∆U = q - W ∆U = 0 (since no heat is exchanged, q = 0) + 500 J

∆U = -500 J

So, the change in internal energy (∆U) for the gas is -500 J.