## Using Kc vs Kp

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Nathan Barger 3B
Posts: 18
Joined: Fri Sep 25, 2015 3:00 am

### Using Kc vs Kp

When exactly do you use Kc and when exactly do you use Kp. Although I understand that if you are given molar concentrations you should use Kc and if you are given partial pressures you should use Kp but if a question asks to simply write the expression for the equilibrium constant for the reaction and no numbers or concentrations are given but the gas equation is given, which do I use? I thought we were supposed to simply use Kc but the answer given in the back says to use Kp. is this because the entire equation involves nothing but gases?

Chem_Mod
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### Re: Using Kc vs Kp

If there are only gases then Kp is appropriate. You would only be able to use Kc if the total volume of the container were given.

Kiara Quinn 3B
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Joined: Sat Jul 09, 2016 3:00 am

### Re: Using Kc vs Kp

Would there be a case in which you would have to use both Kc and Kp at the same time?

Joshua Baysa 1J
Posts: 10
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Using Kc vs Kp

I don't think you would have to use both Kc and Kp simultaneously (at least for this class). I'm not 100% sure but it doesn't seem like it. However, there is a way to manipulate the formulas in order to get both Kc and Kp in the same equation