Question

What form of matter is heat?

Answer 1

Hint : We know that when heat is supplied to a system, it is used to do work and increase the temperature of the system. Heat is known as the energy in transit. In other words, it is defined as the energy which is being transferred from one place to another or from one system to another.

Complete Step By Step Answer:
We know that from the first law of thermodynamics that a heat given to a system is used to increase the internal energy of the system and to do work by the system. We can represent this mathematically as $Q\text{ }=\text{ }\Delta U\text{ }+\text{ }W$ . Where $\Delta U$ is the change in internal energy, $W$ is the work done, $Q$ is the heat supplied to the system.
So, the heat given to a system gives the system the ability to do work, which is basically the definition of energy. Energy is the ability to do work. The heat given to the system also increases the temperature of the system. Heat can be given out from a system, and as a result, the temperature can be reduced and the work done in this case can be considered as negative as per convention. So, we can say that heat is a form of energy in transit.

Additional Information:
In a thermodynamic system, there can be two types of work.
The isochoric work- In this type of work, the volume of the system remains constant. This kind of work includes the shaft work done by a compressor fan can be considered as an Isochoric work.
The boundary work- In this type of work done by the system, the volume of the system is expanded against a certain external. Expansion of the walls of a gas container against a constant external pressure is an example of this.

Note :
Note that the heat can be transferred across various states of matter through conduction, convection and radiation. In this radiation is the fastest process, while the conduction is the slowest mode of heat transfer.