Concept:
The internal energy (\(U\)) of an ideal gas is a state function that depends exclusively on the temperature (\(T\)) of the system. According to the kinetic molecular theory, for an ideal gas, the internal energy is directly proportional to the temperature.
Step 1: Analyze the thermodynamic process.
The problem states that the gas is expanded at a "constant temperature." This identifies the process as an isothermal expansion.
Step 2: Determine the change in temperature (\(\Delta T\)).
Since the temperature remains constant throughout the entire expansion process, the change in temperature (\(\Delta T\)) is equal to zero.
Step 3: Calculate the change in internal energy (\(\Delta U\)).
For an ideal gas, the change in internal energy is given by the formula \(\Delta U = n C_v \Delta T\). Since \(\Delta T = 0\), it follows that \(\Delta U = 0\). Therefore, the internal energy does not change during this process.