- #1
Cathr
- 67
- 3
Homework Statement
I am always confused about how to correctly write the functions U, H, F, G when they're not depending on the usual variables p, V, T, S - same question for Q and W.
For example, we have to calculate the temperature variation of a small surface of water when we isentropically change the surface. The variables are A=a-bT (superficial tension constant), T (temperature) and E (surface). It is given that the elemeptary work dW=AdE.
Homework Equations
dU=TdS+AdE (why don't we add -pdV too? sometimes we do)
dF=-SdT+AdE
dH=TdS-EdA
dG=-SdT-EdA
The Attempt at a Solution
Now we know that, to solve this, we must find the right state function between the 4.
I am really confused about the EdA and AdE part. How to know how to write these equations correctly, without doubting if I'm right?
This is just an example, but this is the kind of problem I have for more cases. If there is a generalised way of reasoning to understand them all?
For the classic 4 variables there is the mnemotic scheme of Born so there's no problem.