Chemistry / Unit 10 Chem 1774 short lesson, about 20 seconds
Kp vs. Kc Relationship
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The idea
Kp uses partial pressures, Kc uses concentrations, and the two relate through Kp = Kc(RT)^Δn, Δn being the change in gas moles.
In practice
For N2 + 3 H2 ⇌ 2 NH3, Δn = 2 − 4 = −2, so Kp and Kc differ by (RT)⁻².
Where people slip
Using total gas moles for Δn, rather than products minus reactants, gives a wrong factor.
Your place on the trail
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