In an isothermal process, the internal energy

Concept:

Internal Energy (U):

• The internal energy of a system is the energy contained within the system, including the kinetic and potential energy as a whole.
• Change in internal energy is given as:
• dU = U2 - U1 = mCV(T2 - T1)
• For isothermal process T2 = T1 ⇒ dU = 0, ∴ U2 = U1
• The internal energy of an ideal gas is a function of absolute temperature only. 
• In the case of an isothermal process, there is no change in temperature so the change in internal energy is also zero.
• So internal energy of the system remains constant.

Additional Information

F or an ideal gas

U = f(T) only, where T is absolute temperature.