HEAT FORM 5 PART 1

heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter (e.g. conduction, radiation, and friction).^[1]

Like thermodynamic work, heat transfer involves the surroundings of a system, as well as the system itself, and so is not a property of the system alone, though it contributes to change in the system's internal energy, which is a property of the system alone. This is distinct from the ordinary language usage of the word 'heat' as a property of a system in itself.

The quantity of energy transferred as heat in a process is the amount of transferred energy excluding any thermodynamic work that was done and any energy contained in matter transferred. For the precise definition of heat, it is necessary that it occur by a path that does not include transfer of matter.^[2] For example, radiative heat transfer can co-occur with matter transfer.

Though not immediately by the definition, but in special kinds of process, quantity of energy transferred as heat can be measured by its effect on the states of interacting bodies. For example, respectively in special circumstances, heat transfer can be measured by the amount of ice melted, or by change in temperature of a body in the surroundings of the system.^[3] Such methods are called calorimetry.