## Kc and Kp [ENDORSED]

Wenxin Fan 1J
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Joined: Thu Jul 13, 2017 3:00 am

### Kc and Kp

If a question contains a chemical formula that only consists of gasses, will it be acceptable to write the equilibrium constant or expression as either Kc or Kp if it does not specify. The book had examples of both. Is there a go-to if the question does not specify?

For example, chapter 11 question 3 did not specify but the answer was in terms of pressure. Question 9 specified Kc.

Chem_Mod
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### Re: Kc and Kp  [ENDORSED]

If the number of moles of reactants and number of moles of products are the same, then Kc is equal to Kp. Typically, if the balanced chemical equation is written in the gaseous state, you should use Kp. If concentrations, then you should use Kc. The two equilibrium constants are related by the expression $\mathit{K}_{p}=\mathit{K_{c}}(RT)^{\Delta n}$ where $\Delta n$ is the difference between the number of product moles and reactant moles.