During an isothermal expansion of an ideal gas, the gas performs 500 J of work on its surroundings. What is the change in internal energy (ΔU) of the gas and the heat (Q) absorbed?
Answer and explanation
Correct answer: B. ΔU = 0 and Q = +500 J
For an ideal gas, internal energy depends solely on temperature: U = (3/2)nRT. In an isothermal process, temperature is constant (ΔT = 0), so the change in internal energy is zero (ΔU = 0). By the first law of thermodynamics (ΔU = Q - W), 0 = Q - W => Q = W = +500 J (the gas absorbs 500 J of heat from the reservoir to perform 500 J of expansion work).
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