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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: zmasterflex on March 04, 2014, 02:40:56 PM

Title: Equilibrium constant
Post by: zmasterflex on March 04, 2014, 02:40:56 PM

What is the relationship between the equilibrium constant of a reaction (Kc) and the rate constants for the forward (Kf) and reverse reactions (Kr)?

If the law of mass action = Q = Kc = products/reactants, then the answer should presumably be Kc = Kr/Kf.. Answer given is Kc=Kf/Kr Why?
thanks

Title: Re: Equilibrium constant
Post by: Kate on March 04, 2014, 03:49:08 PM

This has to do with kinetics or, better yet, with the relationship between thermodynamics and kinetics.

Suppose you have the reaction C ::equil:: D

Then,

v_f = k_f[C]

v_r = k_r[D]

At equilibrium, v_f = v_r, so k_f[C] = k_r[D]

Since [D]/[C] = K_c, then k_f/k_r = K_c