Heat

Heat is the interaction among systems that takes place by virtue of their temperature difference whenever they correspond. This definition explains the process by which a heat interaction is acknowledged. It identifies two conditions that should be satisfied for a heat interaction among systems to take place:

(a)  Temperature difference.
(b)  Communication.

The two cases should be fulfilled concurrently; the absence of either need will mean the absence of heat.

In order to be helpful, the definition of heat should be joint with a statement about how heat is to be measured.  We defined a standard system (a particular quantity of any substance) and a standard procedure that the system was caused to undergo by the interaction (a particular change of elevation in a standard gravitational field). The magnitude of the work communication causing this procedure that is the work, was then determined as the unit of work, and was specified a name, one newton metre.

Corresponding steps are required in defining a measurement process for a heat communication. The standard system is 1 kg of water at a temperature of 14.5^oC and a pressure of 1 atm. The standard process includes placing this standard system into communication with a second system at a distinct temperature. A heat interaction takes place that causes the temperature of the standard system to increase to 15.5^oC. The magnitude of these at interaction in this operation is stated as one kilocalorie (1 kcal).

It is found experimentally that the second system discussed above has to be at a temperature higher than 15.5^oC. This is an example of the rule which a heat interaction tends to decrease the temperature difference that causes the interaction.

Whenever a system H at a higher temperature corresponds with a system L at a lower temperature, the heat interaction might be determined as follows: Suppose L to be substituted by a number of standard kilograms of water that increase in temperature from 14.5^oC to 15.5^oC as H performs the similar process as whenever communication with L. The number of kilograms is the needed magnitude, in k cal. Obviously, it is not essential actually to carry out this procedure.