What happens to the internal energy of an ideal gas during an isothermal expansion process?

💡 Solution & Explanation

During an isothermal expansion process of an ideal gas, the system is maintained at a constant temperature through thermal contact with a heat reservoir. Because the internal energy of an ideal gas is strictly a function of its absolute temperature, keeping the temperature constant ensures that the internal energy remains unchanged throughout the process. Any heat absorbed by the gas is completely converted into work done on the surroundings.