partial pressures vs. concentrations

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melissa_dis4K
Posts: 106
Joined: Fri Sep 28, 2018 12:28 am

partial pressures vs. concentrations

Postby melissa_dis4K » Mon Jan 21, 2019 10:13 pm

I've noticed that when all the species are in the gas phase, the book has been using partial pressures and then converting them into concentrations using the ideal gas law and the ice table, so my question is when calculating the equilibrium constant for a reaction with all species in gas phase should we use Kp or it depends on the question, meaning we could use both Kc or Kp?

Daniel Lai
Posts: 65
Joined: Fri Sep 28, 2018 12:28 am

Re: partial pressures vs. concentrations

Postby Daniel Lai » Mon Jan 21, 2019 10:21 pm

I think it depends on what they are asking for. If they do not specify, just make sure its clear which one you are finding.

Tessa Lawler 1A
Posts: 57
Joined: Fri Sep 28, 2018 12:18 am

Re: partial pressures vs. concentrations

Postby Tessa Lawler 1A » Mon Jan 21, 2019 10:39 pm

I also think it depends on what the question is asking for. I'm pretty sure that on the exam, Professor Lavelle will specify which one he's looking for. Since the only two states we can use in Kc/Kp calculations are gases and aqueous solutions anyway, we're bound to have problems with only gases reacting where we're only asked to find the Kc, or vice versa. In that case, there's no need to do both calculations when only one value is required.

Ibrahim Malik 1H
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Joined: Fri Sep 28, 2018 12:27 am
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Re: partial pressures vs. concentrations

Postby Ibrahim Malik 1H » Mon Jan 21, 2019 11:39 pm

Kp can actually be converted into Kc using the equation Kp=Kc(RT)^delta n, showing that Kp and Kc are not always interchangeable. You solve for the equilibrium constant using what the question gives you (whether it is Kp or Kc), unless noted otherwise.


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