- #1
siresmith
- 5
- 0
Equation apply to reversible only or not??
My thinking must be faulty somewhere, but I can't work out what's gonig on...
The equation
Tds = du + pdv and
du = dq + dw
are supposed to be valid for all processes right?
yet dw = -pdv only for reversible cases, yes?
So how do you prove that du = Tds + fdx
given that fdx = dw (for a stretched wire) if you don't know if its a reversible process?
As fdx = dw can only be equated with the -pdv if its reversible.
[or similarly, ydA in place of fdw for the surface tension of a droplet. Are you just supposed to know these are reversible?]
Secondly, is Cp, 'heat capacity at constant pressure' independent of pressure?
Anybody know the answers??
My thinking must be faulty somewhere, but I can't work out what's gonig on...
The equation
Tds = du + pdv and
du = dq + dw
are supposed to be valid for all processes right?
yet dw = -pdv only for reversible cases, yes?
So how do you prove that du = Tds + fdx
given that fdx = dw (for a stretched wire) if you don't know if its a reversible process?
As fdx = dw can only be equated with the -pdv if its reversible.
[or similarly, ydA in place of fdw for the surface tension of a droplet. Are you just supposed to know these are reversible?]
Secondly, is Cp, 'heat capacity at constant pressure' independent of pressure?
Anybody know the answers??