## Van't Hoff Temperature Dependence

$\ln K = -\frac{\Delta H^{\circ}}{RT} + \frac{\Delta S^{\circ}}{R}$

Andrew F 2L
Posts: 103
Joined: Sat Aug 17, 2019 12:17 am

### Van't Hoff Temperature Dependence

Can someone explain to me why we are taking the natural log of Temperature in Van't Hoff's equation? I'm confused as to what the equation also is trying to convey also because I was confused about the in class example. Thank you!

Philomena 4F
Posts: 27
Joined: Wed Feb 27, 2019 12:16 am

### Re: Van't Hoff Temperature Dependence

He mentioned in lecture that you apply this equation to calculate K at different temperatures if deltaH is given.
He broke down the equation to the ln(K2/K1) = -deltaH/R (1/T2 - 1/T1) with the assumption that deltaH is constant.

sarahforman_Dis2I
Posts: 109
Joined: Sat Aug 17, 2019 12:18 am

### Re: Van't Hoff Temperature Dependence

Andrew F 2L wrote:Can someone explain to me why we are taking the natural log of Temperature in Van't Hoff's equation? I'm confused as to what the equation also is trying to convey also because I was confused about the in class example. Thank you!

The reason you take ln(K) is because you are assuming that the reaction is at equilibrium, meaning delta G is equal to zero.

You have the two equations ∆G= ∆Gnot +RTln(Q) and ∆Gnot=∆Hnot-T∆S
At equilibrium, Q=K and ∆G=0
You can then solve for ∆Gnot and set the two equations equal to each other. This is what gives you the ln(k) in the equation. I hope that this helps!

Marni Kahn 1A
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Joined: Thu Jul 25, 2019 12:17 am
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### Re: Van't Hoff Temperature Dependence

You have the natural log in the equation already given ∆G=∆G°+RTlnQ, and then ∆G°=-RTlnK at equilibrium(∆G=0 at equilibrium)

Emily Burghart 1k
Posts: 50
Joined: Wed Sep 18, 2019 12:17 am

### Re: Van't Hoff Temperature Dependence

What equation do you use if you are not sure if the equation has a $\Delta G$ equal to 0?

Is there a way to check that $\Delta G$ is 0 if it is not explicitly stated in the problem?

What happens if you use the equation for a reaction that is not at equilibrium?