Work done - thermodynamics:
A free expansion process is a process in which system expands freely without experience any resistance. I.E. is constant at the time of state change this process is highly irreversible because of eddy flow of fluid during the process and there is no heat transfer at all.
dU = 0; dQ = dW (For reversible process)
dQ = 0; dW = 0; T1 = T2; dU = 0