Monday, July 15, 2019

carnot cycle - 2nd law of thermodynamics' violation?



According to 2nd law of thermodynamics, it is not possible to convert heat 100% into work.


Well, investigating about the Carnot Cycle, I have found out that in the first step, the process is to heat a gas without rising its temperature, this is, converting all the heat into work. Isn't this a violation of the 2nd law?


I clearly don't understand something about the law or about the Carnot Cycle. I would like to know where I'm failing in my understandig. Thank you.



Answer



It is possible to convert heat 100% into work provided that something else happens to your heat machine (i.e. the heat-to-work conversion system). In your case, the gas has expanded, so the state of the heat machine is not the same as in the beginning.


The 2nd law of thermodynamics states that it is not possible to convert heat 100% into work AND have the heat machine in a state that is identical to its initial state.


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