# K, Kc and Kp: Chemical Engineering Work

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#1
I am a little unclear on the distinction between K, Kc and Kp in chemical equilibria.

I am aware that you can write: Rate = Kc * Conc(A)^a * Conc(B)^b

I also know how to calculate Kc and Kp and that they can be related to each other through the Ideal Gas Equation.

What I am unclear of is whether I can use Kp in the above equation and how that would work. for example, would the following be true?

Rate = Kp * Partial Pressure(A)^a * Partial Pressure(B)^b

Lastly, how does K link to Kp and Kc?

With the Arrhenius Equation we can say: K = A*exp(-Ea/RT)

Would this be equally valid for Kp and Kc?

Thank you for your help and sorry if my thoughts are a little jumbled!
0
6 years ago
#2
I think the first 'kay' you are referring to is k (the rate constant - lower case k) whereas Kc is the equilibrium constant in terms of concentrations ; Kp is the equilibrium constant expressed in terms of partial pressure of gases
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6 years ago
#3
Kc and Kp can be both used for gaseous mixtures. k from the rate equation describes completely different thing, it just happens to use the same letter as a symbol.
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6 years ago
#4
You are mixing up the Rate constant K with equilibrium constant Kc Kp

They are quite different. You cannot put Kc or Kp​ into the rate equation.
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