We start by presenting an overview of the various definitions of heat and work found in the literature. Then, we consider several examples for analysis and show that the theory of Thermodynamics requires a precise definition of such quantities. The comparison regarding the Second Law of the system-based and surroundings-based definitions of heat and work is undertaken leading to the conclusion that the definitions of such concepts should be based on variables external to the system.
work; heat; first law; second law; irreversible processes
