Confusion on different versions of the Van't Hoff equation?


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Nicole Anisgard Parra 2H
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Joined: Sat Jul 22, 2017 3:01 am

Confusion on different versions of the Van't Hoff equation?

Postby Nicole Anisgard Parra 2H » Mon Feb 12, 2018 6:55 pm

The textbook has the Van't Hoff equation as lnK2/K1= delta H/R + {1/T1-1/T2}, while the version we talked about in class has lnK2/K1=-delta H/R + {1/T2-1/T1}. Aside from the delta H factor being negative, and the T's being switched, which are the two differences, which version should we be using in our calculations? Do they produce the same answer?

Chris Lamb 1G
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Joined: Fri Jun 23, 2017 11:39 am

Re: Confusion on different versions of the Van't Hoff equation?

Postby Chris Lamb 1G » Mon Feb 12, 2018 7:42 pm

That is just two ways of writing the same equation. They may look different, but the negative sign is just on different sides of the equation. You can use properties of logs to see why the k2/k1 becomes k1/k2.

Kyle Alves 3K
Posts: 46
Joined: Thu Jul 27, 2017 3:01 am

Re: Confusion on different versions of the Van't Hoff equation?

Postby Kyle Alves 3K » Tue Mar 13, 2018 10:14 pm

Refers to calculating K at different temperatures
At T1: lnK1 = -(deltaH/RT1) + (deltaS/R)
At T2: ln K2 = -(deltaH/RT2) + (deltaS/R)

leading to
lnK2 - lnK1 = ln(K2/K1) = -(deltaH/R)(1/T2 - 1/T1)
just factoring the negative into the temperature will switch the two
Last edited by Kyle Alves 3K on Tue Mar 13, 2018 10:18 pm, edited 1 time in total.

Masih Tazhibi 2I
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Joined: Fri Sep 29, 2017 7:06 am

Re: Confusion on different versions of the Van't Hoff equation?

Postby Masih Tazhibi 2I » Tue Mar 13, 2018 10:17 pm

You can use either version of the equation. It was discussed in class that scientists just prefer not having negative signs in their equations if they can avoid it, so they sometimes reframe the equation to that end. However, both are perfectly fine as long as you keep your k and T values consistent.

Pooja Nair 1C
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Joined: Thu Jul 13, 2017 3:00 am

Re: Confusion on different versions of the Van't Hoff equation?

Postby Pooja Nair 1C » Fri Mar 16, 2018 1:11 am

Both equations will give you the same answer, and you can derive the equation we use from the one in the book. We use the one that we do because it's simpler, so you should be fine using the one Lavelle taught us


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