quality:correction, information:extraction
Direction of spontaneous processes

However, for some non-isolated systems which can exchange energy with their surroundings, the surroundings exchange enough heat with the system, or do sufficient work on the system, so that the processes occur in the opposite direction. In such a case, the reverse process can occur because it is coupled to a simultaneous process that increases the entropy of the surroundings. The coupled process will go forward provided that the total entropy change of the system and surroundings combined is nonnegative as required by the second law: Δ S = Δ S + Δ S ≥ 0. For the three examples given above: