[hsp]

I have two simple equilibrium questions that I just need a bit of reassurance on, but first I need to ask another basic question:

What K is represented in the equation ΔG = -(RT)lnK. Can it be both Kp and Kc? In my chemistry notes i've seen examples where it is used as Kp but then when the formula is first introduced it says it's the equilibrium constant - which i assumed meant Kc?

Does this mean that the equilibrium constant can be either Kp or Kc?

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Q1. A gas A can dimerise to A2, which is also a gas. The standard molar free energies of formation of A (g) and A2 (g) are 53.63 kJ/mol and 97.64 kJ/mol, respectively. What is the value of Kp for the reaction written as follows at 25ºC?

2A → A2

To begin with to get ΔGfo i did, ΔGfo = 97.64 - (2x53.63) = -9.62kJ/mol.

ΔG = -(RT)lnK
-9.62x1000 = -(8.314x298.15)lnK
Kp=e^(-9.62x1000/-[8.314x298.15])
Kp=48.5574...

Is this correct? or is the Kp actually the Kc, and i need to move on to use the formula Kp=Kc(RT)^Δn?

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Q2. Given that ΔGfo for NH3 = -16.67 kJ/mol, calculate the equilibrium constant for the following reaction at 305 K:

N2 (g) + 3 H2 (g) → 2 NH3 (g)

For this question I'm unsure whether the equilibrium constant is Kc or Kp? My tutor said that it's a gas to it is fine to remain as Kp?

Working:

ΔG = -(RT)lnK
-16.67x1000 = -(8.314x305)lnK
Kp =e^(-16.67x1000/8.314x305)
Kp = 716.186

Is that the final answer or do i move on to use Kp=Kc(RT)^Δn, in which case:

Kp = Kc(RT)^Δn
716.186 = Kc(8.314x305)^-2
Kc = (716.186/([8.314x305]^-2)
Kc = 4605168721
Kc = 4.61x10^9

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I'm in my first year at uni and have done very very little chemistry before this so any help would be greatly appreciated! I'm not necessarily looking for answers, more so help on what or where i've gone wrong and where i'm confused.

Thanks heaps!

[hsp]

If anyone wants to know, the first one was correct...

the second answer i forgot to times the deltaG by 2 because the products have 2 moles.
Dang. Surely someone could have helped out?

Thanks to anyone who thought about it ha.