[CKabes]

For the process CH₃OH(l) CH₃OH(g)
ΔG°= 4.3 kJ/mol at 25°C. What is the vapor pressure of CH₃OH(l) at 25°C in mm Hg?

Can someone please provide an equation or a start?
I thought I would find entropy, but I would require ΔH, or I could find ΔH if I could first find ΔS, and then possibly use the Clausius-Clapeyron equation to find vapor pressure?

[UG]

Can someone please provide an equation or a start?

Yup, there is an equation which relates ΔG° to the equilibrium constant K

[CKabes]

ΔG=-RT ln(K) ?

How do I procede after I find K?

[UG]

How do I procede after I find K?

Well, what is the expression for K for the reaction CH₃OH(l)  CH₃OH(g) and what does it express?

[CKabes]

K is the ratio of product to reactant at equilibrium where the forward reaction rate is equal to the reverse. The equilibrium expression for this reaction would be:

CH₃OH(g) / CH₃OH(l), however because CH₃OH(l) is a pure substance, the Equilibrium Expression would simply be K = CH₃OH(g)

Is that correct?

[UG]

CH₃OH(g) / CH₃OH(l), however because CH₃OH(l) is a pure substance, the Equilibrium Expression would simply be K = CH₃OH(g)

Ok, so you have K is equal to some value. What does this value signify, is it a concentration, a pressure, a ratio perhaps?

[CKabes]

Here's what I said earlier:

K is the ratio of product to reactant at equilibrium where the forward reaction rate is equal to the reverse

[curiouscat]

Here's what I said earlier:

K is the ratio of product to reactant at equilibrium where the forward reaction rate is equal to the reverse

" ratio of product to reactant" doesn't mean anything much quantitatively.

e.g. What's "ratio of you to me"? Our weights? Our heights? Our money? Our ages?

Get the point?

[CKabes]

Alright, let me try again,

K is the ratio of the concentration of products to reactants in moles at a certain temperature

[curiouscat]

Alright, let me try again,

K is the ratio of the concentration of products to reactants in moles at a certain temperature

That's a specific case. It'd be wrong in general.

e.g. It's not even consistent with this that you wrote earlier:

because CH3OH(l) is a pure substance, the Equilibrium Expression would simply be K = CH3OH(g)

[Stovn0611]

For the equation ΔG=-RT ln(K), K represents the Kp equilibrium constant - think about what Kp is a ratio of

[CKabes]

K_p is the partial pressure of the products devided by the partial pressure of the reactants?

[Stovn0611]

Yes exactly(and it works the exact same way as for concentrations and you have to take the partial pressure to the power of whatever the coefficient of that substance is in the reaction)

For example, in this reaction:

N₂ + 3H₂ -> 2NH₃

Kp = P_NH3²/(P_H2³P_N2)

So in this reaction, CH3OH(l) CH3OH(g)

Kp = P_CH3OH since the liquid form will not be able to exert any pressure