Why is work not a state function?

[reising1]

I thought that state functions are properties that don't depend on the path taken to reach that particular value. Is work a state function or not? It seems that the internet says heat and work are NOT state functions, whereas energy is.

Can someone give a way to determine, for any property, if it is a state function or not. I feel like there's an easier way to think about this rather than to just memorize, for every property, if it's a state function or not.

And, specifically, with work, isn't it W = Force * displacement? So if I take some crazy path but end up back where I started, the work should be 0, so doesn't that mean it's a state function?

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[UCFMD]

State functions can be measured without prior knowledge of the system. By needing to know the displacement and the force, its by definition not a state function. An example of a state function is hair color. I can tell what color hair you have without any other knowledge.

Work can be conserved as you've mentioned above with your example of a conservative force. But just because it adds up to zero doesn't mean its not dependent upon on other factors.

Its zero because it is dependent upon the path, not the other way around. You can also think about this in terms of chemistry: is work related to the change in energy when a system goes from one state to another? Absolutely, therefore it is dependent upon the state and not a state function. Also it may be easier just to remember the seven or so important state functions. Come up with a funny acronym or something.

 

[reising1]

Thanks for the explanation, and I do understand that with Work, since displacement is needed, it is not a state function. But I still don't understand how to know for any property if it's a state function or not. I'm not understanding the general rule.

Certainly, energy depends on many things. I can't just walk up to something and know it's energy without knowing other properties about it (ex. how much work is being done in that system? how much heat is being released?) and yet energy is a state function.

So maybe you're right, I should just memorize them. Can you list the important state functions?

 

[UCFMD]

Sure, they are:

1. Temperature
2. Volume
3. Density
4. Enthalpy
5. Entropy
6. Pressure
7. Internal energy
8. Gibbs free energy

The general rule is that these are physical properties at an equilibrium state that are pathway independent. You have to go through each one to make sense of them, but basically for each one, if you take a system at point X and move it to point Y, the path in which you move makes no difference. In contrast, heat and work are what drive the path, they're the reason a change in state occurs. If you need help with one of those specifically, I can try to help you out.

 

[reising1]

Thanks so much! I'll try to work on mnemonics for these lol.