Science Olympiad Thermodynamics Practice Test 2026 – All-In-One Study Guide to Master Your Competition!

In an isothermal process, the temperature of the system remains constant. For an ideal gas, the internal energy is solely a function of temperature. Since the temperature does not change during an isothermal process, the internal energy also remains unchanged.

This means that any heat added to the system is fully balanced by an equal amount of work done by the gas. The first law of thermodynamics states that the change in internal energy (ΔU) is equal to the heat added to the system (Q) minus the work done by the system (W). In an isothermal process for an ideal gas, though, since the internal energy does not change, the equation simplifies to ΔU = 0, affirming that internal energy is indeed constant.

Therefore, the correct understanding in this context is that the internal energy of an ideal gas remains constant during an isothermal process.