Question

Gibbs and Work

Answer 1

That's not correct, is it? Here are a bunch of equations for reference:\[\rm dG = Vdp - SdT\]\[\Delta G = \Delta H - T \Delta S\]\[\Delta H = \Delta U + \Delta (PV) \]

Answer 2

What are we doing here? What's the question?

Answer 3

\(\sf \Delta G = [\Delta U + \Delta(PV)] - T\Delta S \)

Answer 4

hmm

Answer 5

@Zela101 We're trying to explain the fact that the change in Gibbs free energy is the maximum possible work of non-expansion that can be extracted by a system. (I still don't understand what that means though.)

Answer 6

The change in potential energy is defined as\[\Delta U = -w\]So these two terms are very related.

Answer 7

yes

Answer 8

\(\sf \Delta U = \Delta A+T\Delta S \) Helmholtz Free Energy
\(\sf \Delta G = [\Delta U + \Delta(PV)] - T\Delta S \)
\(\sf \Delta G = \Delta A + T\Delta S + \Delta(PV) - T\Delta S \rightarrow \Delta G = \Delta A + \Delta (PV)\)

Answer 9

hmmm that looked pretty in my mind, but not so in paper

Answer 10

\(\sf \Delta PV = \Delta G - \Delta A \)

Answer 11

What do you think, are we going anywhere?

Answer 12

Not quite sure. I don't know what Helmholtz free energy is apart from the definition, so it's going to be hard for me to relate

Answer 13

HAHA if we think of it as the energy within the system itself, then would that help us in terms of energy transfer?

Answer 14

I mean a non-expansion from that last line of equation I did would show a + G and whatever value of internal system A

But here is what confuses me. I thought G is the system as well.

Answer 15

I thought I remember a schematic diagram a while back from hyper physics about this, let us look it up

Answer 16

HEY LOOK I found it http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/helmholtz.html

Answer 17

nice lol

Answer 18

brb mechanics is my first wife

Answer 19

what do you think, Zale?
I think I was close. With the G = U -TS + PV

Answer 20

yeah, we did say something like this in the chat, like we're removing the heat which is being used to increase the entropy and nothing else http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/imgheat/gibb.gif

Answer 21

Combining Gibbs energy G = H-TS, and the enthalpy H = U +PV and getting G = U + PV -TS seems right. I agree nin.