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The Second Law of thermodynamics allows work to be transformed fully into heat, but forbids heat to be totally converted into work. If heat could be transformed fully into work it would violate the laws of entropy.

What are the laws of entropy that would be violated if heat could be fully transferred into work?

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  • $\begingroup$ Clausius $\oint \frac{\delta Q_{rev}}{T}=0$ $\endgroup$ – hyportnex Aug 22 '18 at 23:39
  • $\begingroup$ @hyportnex That looks like it should be an answer, not a comment $\endgroup$ – David Z Aug 23 '18 at 0:10
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    $\begingroup$ The second law doesn’t say that. Please look it up relative to heat and work, and see what you left out. $\endgroup$ – Chet Miller Aug 23 '18 at 1:47
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Heat can be totally converted to work in a process. That does not violate the second law. An example is the isothermal expansion of an ideal gas. But it is not possible to have a thermodynamic cycle whose only effect is to completely convert heat to work. That would be a violation of the Kelvin-Plank statement of the second law, which states:

“It is impossible to construct a device which operates on a cycle and produces no other effect than the production of work and the transfer of heat from a single body”.

Hope this helps.

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