It has been determined, as stated in the second law of thermodynamics, that the entropy is a state function: It depends only upon the state that the system is in, and not what path the system took to get there. This is in contrast to the amount of energy added as heat (𝛿 Q) and as work (𝛿 W), which may vary depending on the path. In a cyclic process, therefore, the entropy of the system at the beginning of the cycle must equal to the entropy at the end of the cycle (because the entropy is a state function), Δ Δ S = 0 , regardless of whether the process is reversible or irreversible. In irreversible cases, the net entropy is added to the system reservoirs ( Δ Δ S surr > 0 ) per thermodynamic cycle while in reversible cases, no entropy is created or added to the reservoirs.