According to thermodynamic first law, change in internal energy of a system equal to the net heat transfer into the system minus net work done by the system. So, Q=+ ve adds energy to the system and W=+ ve takes energy from the system ΔU=Q−W Here, ΔU= internal energy If, ΔU=−W, then Q=0 i.e. no heat is exchanged. ∴ The process is adiabatic. Hence, change in internal energy is equal to adiabatic work.