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I am trying to understand the concept of "entropy" in thermal engineering point of view.

I have basic idea about "entropy" i.e. the change in entropy is used to determine the direction in which a given process will proceed.

However following two more definition (of entropy generally available in text books) are confusing and not allowing me to really understand it.

Can anyone explain me above definitions rather entropy concept with simple examples with mathematical explanations…

- “Entropy can also be explained as a measure of the unavailability of heat to perform useful work”. Or “Entropy quantifies the energy of a substance that is no longer available to perform useful work”.

- “Entropy is sometimes referred to as a measure of the inability to do work for a given heat transferred.”

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# Entropy: measure of amount of energy unavailable to do work?

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