Ah, you are wrestling with that equilibrium constant conversion! I always remind myself that Δn is simply moles of gaseous products minus moles of gaseous reactants. The formula Kp = Kc(RT)^(Δn) is reliable, but one must be very careful to count *only* the gaseous species in the balanced equation; solids and liquids do not count. In the lab last week, I nearly made that mistake with the decomposition of CaCO₃, forgetting that the solid CaO doesn't enter the Δn calculation.
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