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In every textbook I read, it says that heat is a form/type of energy... but in lecture, my professor said, that there is no such energy as heat and that heat is just a method by which we can transport energy to another system. Do these 2 statements say the same and I'm just reinterpreting the first one badly. If I were to say in my own words what heat is just based on the textbook's definition, I'd say that heat is energy, that... But if I were to say it by the lecturer words, I'd say that heat is a disordered transfer of energy, not energy itself. What's more correct?

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    $\begingroup$ No, heat is not the same as thermal energy. Heat is energy transfer other then matter transfer or thermodynamic ( =volume or nonvolume ) work, i.e. mostly, but not limited to, transfer of thermal energy as kinetic and potential energy of molecules/atoms. $\endgroup$
    – Poutnik
    Oct 5, 2020 at 9:53
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    $\begingroup$ Yes, they mix it up. Heat is a kind of energy, but at the special circumstances. It is energy on the move, the energy flow, aside of that excluded above. Note that we write $\Delta U = Q + A$, not $\Delta U = \Delta Q + \Delta A$. Also, Q can be negative, while thermal energy cannot be. $\endgroup$
    – Poutnik
    Oct 5, 2020 at 9:57
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    $\begingroup$ Small correction: Rather energy transfer than flow, as heat has the same unit as energy [J]. Energy flow would be rather [J/s=W], or [J/s/m2=W/m2], depending on context. $\endgroup$
    – Poutnik
    Oct 5, 2020 at 10:05
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    $\begingroup$ I agree with others. Heat is energy in transit. However, I would not really say the first is totally wrong. It becomes rather semantic. I am more concerned of the opposite, when a Delta over a reaction arrow is taken erroneously as high T instead of the fact that there must be a transit of energy from the surrounding to the reaction vessel. And this transfer, the heat, requires energy, of course. $\endgroup$
    – Alchimista
    Oct 5, 2020 at 10:06
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    $\begingroup$ As you know that this energy gets transfered in the form of infrared rays so heat is more of a layman word $\endgroup$
    – Stack3002
    Oct 5, 2020 at 15:10

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