The surroundings-based definitions of heat and work, which
Gislason and Craigs describe as an obvious extension of the
global formulation, identify -2,-AB,-Q as heat and ‘*2,-.A.E?; as work. This article uses the symbols q’ and w’, respectively, for these surroundings-based quantities, and reserves the symbols q
and w for the conventional system-based heat and work. Note
that q’ is the negative of the total thermal energy change, and w’ is the negative of the total mechanical energy change, in the surroundings. They do not necessarily represent energy
transfers across the system boundary as do q and w.