## 5J.15

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

Jordan Young 2J
Posts: 102
Joined: Thu Jul 25, 2019 12:17 am
Been upvoted: 1 time

### 5J.15

To find the equilibrium constant at 150 Celsius, why can't you use △G=-RTlnK? Why do you need to use the Van't Hoff Equation?
For reference:
Calculate the equilibrium constant at 25 C and at 150 C for each of the following reactions, using data available in Appendix 2A:
NH4Cl(s) --> NH3(g) 1 HCl(g)

Ruby Tang 2J
Posts: 102
Joined: Fri Aug 30, 2019 12:15 am

### Re: 5J.15

Data in appendix 2A is specific to the reaction occurring at 25C. Therefore, you can't use △G=-RTlnK for 150C, because the value of △G that you calculated using the appendix data will be different at 150C.

Nick Fiorentino 1E
Posts: 102
Joined: Wed Sep 18, 2019 12:16 am

### Re: 5J.15

There are multiple ways to get the answer, Van't Hoff's equation is one, but you can use △G=-RTlnK and just change the T value when solving for K which would give you K at that temperature

Morgan Carrington 2H
Posts: 54
Joined: Wed Nov 14, 2018 12:22 am

### Re: 5J.15

The data in appendix 2A is measured at STP (25 degrees celsius and 1 atm), so it would work to calculate it for the first portion of the question. However, at 150 degrees celsius you would most likely have to use the Van't Hoff equation. The only way you would be able to use the other equation is if you were able to calculate the Q of the reaction, but in this case you can't.