Sheldunov

I am very grateful to you for your answer! Thank you very much! Could you please explain, how we can prove that entropy is a state variable in general? I know how to do it with ideal gas, but I would be very pleased if you tell me how to do it in general.

Thank you very much for your explanation. Your concept of teaching thermodynamics is quite good and comprehensive and mainly matches ours. Of course we can continue the story of thermodynamics as a play, but my question was about one little precise act of this play. This act is about introducing entropy without the second law. So this little act is about one specific question that matter the most for me in our conversation. The question is can I suggest that we can use only first law to introduce entropy as state variable? And second law is used to determining cardinal property of entropy (growth in closed system in irreversible process).

Yes, but this is not about choosing between statistical or thermodynamical introducing. The question is about specifically THERMODYNAMICAL entropy definition and about using only the first law of thermodynamics in it.

Of course we can introduce entropy in many ways, but the question is can we introduce entropy precisely this way. So you think we can, aren't you? Сould you please explain a little more details. I am not sure whether I understood you correctly.

Am I to understand that entropy is introduced as part of the first law of thermodynamics. And the properties of entropy are determined without a second law. And the second law establishes the condition for the growth of entropy. In other words. Is it possible to say that entropy is introduced as a convenient parameter for determining the inversion of the heat transfer sign, for example?