## Free Energy and Pressure

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

$\Delta G^{\circ}= -RT\ln K$

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

Connie2I
Posts: 29
Joined: Fri Sep 29, 2017 7:07 am

### Free Energy and Pressure

What exactly is the relationship between free energy and pressure? In the notes, it says free energy is dependent on pressure, but I'm not quite sure how.

Tanaisha Italia 1B
Posts: 55
Joined: Fri Sep 29, 2017 7:04 am

### Re: Free Energy and Pressure

I think it might be because free energy is dependent on entropy and enthalpy. Pressure has an inverse relationship with entropy, so if pressure goes up, entropy goes down. This would make the delta G more positive. If pressure decreases, entropy increases, and the delta G becomes more negative.

Kelly Seto 2J
Posts: 30
Joined: Thu Jul 27, 2017 3:00 am

### Re: Free Energy and Pressure

Let's look at our equation dG = dH - TdS
We remember that dH = dU + PdV, so any increase in pressure will result in a larger dH value
If a larger dH value is entered into the equation at constant temperature, we get dG = dH - dS resulting in a large dG, or free energy, value as a result
Therefore, an increase in pressure leads to an increase in free energy

Guangyu Li 2J
Posts: 50
Joined: Fri Sep 29, 2017 7:07 am
Been upvoted: 1 time

### Re: Free Energy and Pressure

The Gibbs free energy depends on pressure as well as on temperature. The pressure dependence of the Gibbs free energy in a closed system is given by the combined first and second laws and the definition of Gibbs free energy as dG=-SdT+Vdp

Hope this helps!

Sarkis Sislyan 1D
Posts: 31
Joined: Thu Jul 27, 2017 3:00 am

### Re: Free Energy and Pressure

Enthalpy is heat under constant pressure, so wouldn't a change in pressure mean pressure isn't being held constant?