Internal energy = State function

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Luyan Zhang - 2D
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Joined: Sat Jul 20, 2019 12:16 am

Internal energy = State function

Postby Luyan Zhang - 2D » Sun Jan 26, 2020 6:15 pm

Why is Internal energy is a state function, but since delta U = heat + work, and neither heat nor work are state functions? Can state functions have non-state function components?

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Re: Internal energy = State function

Postby TarynD_1I » Sun Jan 26, 2020 6:38 pm

Internal energy is a state function I believe because it is independent of the path of the process in question. It has different values at each different state of the system.

Dina Marchenko 2J
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Re: Internal energy = State function

Postby Dina Marchenko 2J » Sun Feb 02, 2020 1:25 pm

It's just the way we calculate things and what we care about looking at based on the definition of the word. Internal energy only looks at the initial and final states and doesn't care about the path taken. Heat and work, on the other hand, we look at the path taken to get the value of both. If the more difficult height is taken to the top of the mountain, for the sake of altitude we don't care since the outcome is the same but for the sake of work done we do care since the harder path required more work and thus that hike has a different value.

I don't think it's necessarily that non-state functions make state functions or vice versa, just the definition of the different variables and what their values represent

Callum Guo 1H
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Re: Internal energy = State function

Postby Callum Guo 1H » Sun Feb 02, 2020 1:37 pm

Internal energy remains constant throughout the reaction (first law of thermo) so it doesn't matter how you get from the initial to final values.

Frank He 4G
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Re: Internal energy = State function

Postby Frank He 4G » Sun Feb 02, 2020 2:22 pm

A different way to think about this is to understand that heat and work are defined as the transfer of a property. You can't say that something is at a certain heat or has a certain work, only that heat was gained or lost, or that work was done by or on it. So if something can't be in a certain state of work or heat, then work and heat are not state functions. Internal energy on the other hand is something we can describe something to have, so it can have different states of internal energy, and thus it is a state function.

As for the equation, it is delta U, not just U. The change in internal energy might be considered a path function.

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