Heat, is when the change in the state of the system originates from the disruption of thermal equilibrium conditions, that is, from the system and the outside world between the existence of temperature difference, we say that there is a thermal interaction between the system and the outside world. As a result of the interaction there is a transfer of energy from a high temperature object to a low temperature object, and the energy transferred is called heat. Heat and work are two different forms of energy transfer that occur along with the change of state of the system, is a measure of the different forms of energy transfer, they are related to the intermediate process of state change, and therefore not a function of the state of the system.