Question

Many students are surprised to learn that the heat in an isothermal process is not zero. which of the following statements best describes why the heat is nonzero?

a. since the volume is increasing the gas does work, so the first law of thermodynamics tells us that the heat must be nonzero.
b. since the volume is increasing the gas does work, so the second law of thermodynamics tells us that the heat must be nonzero.
c. since the volume is increasing the gas does work, so the third law of thermodynamics tells us that the heat must be nonzero.

Answer 1

The heat in an isothermal process is nonzero because as the gas expands and does work, the first law of thermodynamics indicates that heat must be absorbed to maintain constant internal energy as the volume increases.

Step-by-step explanation:

Many students are surprised to learn that the heat in an isothermal process is not zero. The most accurate description of why the heat is nonzero is option (a): since the volume is increasing the gas does work, so the first law of thermodynamics tells us that the heat must be nonzero.

The first law of thermodynamics states that the change in the internal energy of a system (ΔEint) is the sum of the heat transferred (Q) and the work done (W). During an isothermal expansion, because temperature remains constant, the internal energy of an ideal gas does not change (ΔEint = 0). This implies for the first law ΔEint = Q - W. Since work W is done by the gas when the volume increases, Q must be positive to satisfy the equation. This means that heat is absorbed from the surroundings, even though there is no change in temperature.