Why Is Entropy Considered a State Variable?

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bradcliu
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Hi,

My name is Brad and I am a graduate electrical engineering student. Recently I wanted to go back and review and patch some holes in my head about fundamentals of physics. Therefore, I went back to my textbook Physics for Scientists and Engineers with Modern Physics by Serwey and Jewett, 7th ed. I wanted to understand a few questions I had about thermodynamics from years ago, and more specifically, about entropy.

In the text, it states that entropy is a state variable; therefore, we can find some path of reversible process that leads from one state to the next to calculate it. It never stated why it is a state variable or why the reversible path will work for irreversible or real processes. I can certainly calculate it. However, my understanding about this particular section is frustratingly vague. Please enlighten me Q_Q... Thank you.

Brad
 
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i guess entropy of the total universe if not reversible, but entropy of a particular system is reversible.

so if you made your desk messy, you can make it tidy again in a completely reversible fashion, but in the process introducing more entropy into the universe.