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I have referred to some textbooks on Thermodynamics and they more or less explain heat in the following manner:

Consider a system which has some energy content. In order to increase the energy content of the system, i.e. to transfer energy to the system, we can make use of two methods/means/ways - Work and Heat

So I understand heat as the name given to the method/way of transferring energy to a system, where the energy transfer happens via a temperature difference.

However, the textbooks also refer to heat, sometimes, as a form of energy, which doesn't make sense to me. Heat is one of the methods of transferring energy, how can it be a form of energy?

For example, how can a money transfer process be a form of money?

Harshit Rajput
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    See also "Heat is not a noun". "Heat" is too often used to describe what is more precisely defined as thermal energy, enthalpy, or entropy. – Chemomechanics May 16 '22 at 21:01
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    I also note that if you are a native English language speaker, you may be at a disadvantage. Heat is NOT hot. 1000 J of heat can be 10 K, or 100 K, or 1000 K. Assuming a standard state of an ideal gas at 0 K (a chemical engineering concept), temperature is how concentrated that heat is, but temperature does not tell you how much heat a substance contains. – David White May 17 '22 at 00:38
  • @Chemomechanics I too once had this thought that what was the need for giving energy transfer via temperature difference a special name heat, which is similar to what the author of the text that you linked says in one of the paragraphs. There might be historical reasons for the same. – Harshit Rajput May 17 '22 at 07:17

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However, the textbooks also refer to heat, sometimes, as a form of energy, which doesn't make sense to me. Heat is one of the methods of transferring energy, how can it be a form of energy?

You are absolutely correct. Heat is not a form of energy. It is a mechanism by which energy is transferred from one substance, object, etc., to another due solely to temperature difference.

When I was learning about thermodynamics I found a particular description that, at least for me, help differentiate between the energy of something and the transfer of energy (by work or heat) from one thing to another. In this case the transfer of energy by heat. I'd like to share it with you in case it might be helpful. For simplicity, the description is for heat conduction.

Consider two solid objects, one having a higher temperature than the other. Which means the molecules of the higher temperature object 1 have a higher average translational kinetic energy than the molecules of the lower temperature object 2.

The objects are placed in contact with each other. At the interface between the objects the molecules of the higher temperature object collide with the molecules of the lower temperature object. On average, this results in the transfer of kinetic energy from the molecules of the higher temperature object to molecules of the lower temperature object causing the temperature of the higher temperature object to decrease, and the temperature of the lower temperature object to increase.

This transfer of kinetic energy from the molecules of the higher temperature object to the molecules of the lower temperature object is what we mean by heat. But the increase in the average kinetic energy of the molecules of the lower temperature object and decrease in the average kinetic energy of the molecules of the higher temperature object is what we mean by a change in the internal (kinetic) energy of the two objects. Thus the difference between the transfer of energy and the energy itself.

Hope this helps.

Bob D
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