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Kp vs. Kc Relationship

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State

Kp uses partial pressures, Kc uses concentrations, and the two relate through Kp = Kc(RT)^Δn, Δn being the change in gas moles.

Show

For N2 + 3 H2 ⇌ 2 NH3, Δn = 2 − 4 = −2, so Kp and Kc differ by (RT)⁻².

Watch for

Using total gas moles for Δn, rather than products minus reactants, gives a wrong factor.