Since heat (like work) is a quantity of energy being transferred between two bodies by certain processes, neither body “has” a definite amount of heat (much like a body in itself doesn’t “have” work). In contrast, a body indeed has properties (state functions) such as temperature and internal energy. Energy exchanged as heat during a given process changes the (internal) energy of each body by equal and opposite amounts. The sign of the quantity of heat indicates the direction of the transfer, for example from system A to system B; negation indicates energy flowing in the opposite direction.
Although heat flows spontaneously from a hotter body to a cooler one, it is possible to construct a heat pump or refrigeration system that does work to increase the difference in temperature between two systems. In contrast, a heat engine reduces an existing temperature difference to do work on another system.
