Relationship between Equilibrium Constant and Rate Constants

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Charisse Vu 1H
Posts: 101
Joined: Thu Jul 25, 2019 12:17 am

Relationship between Equilibrium Constant and Rate Constants

Postby Charisse Vu 1H » Sun Mar 08, 2020 11:20 pm

How are equilibrium constants and rate constants related? I understand there is an equation relating them, but I would like a conceptual explanation as to how they are related.

Kevin Xu 4F
Posts: 50
Joined: Fri Aug 09, 2019 12:16 am

Re: Relationship between Equilibrium Constant and Rate Constants

Postby Kevin Xu 4F » Mon Mar 09, 2020 1:31 am

An equilibrium constant is a ratio that reflects the molar activities of all the species within a reaction. Since it is hard to accurately measure the molar activities of substances, the best approximation is the molar concentrations, as the two are directly related.

In order to get the equilibrium expression, we have to think of an equilibrium reaction comprising two separate reactions, a forward reaction and a reverse reaction. The forward reaction is dictated by a reaction mechanism of colliding molecules, hence why the coefficient is raised to the power in the equilibrium expressions. This combination of forward and reaction mechanisms is what produces the equilibrium constant ratio of product concentrations to reactant concentrations.

The rate equation is similar to the equilibrium expression in the way that the rate law is calculated using the molar concentrations of the reactant species, However, since there is a complete reaction and no reversible equilibrium, there is usually no fractional proportions of products to reactants, since it is to completion only the concentration of the reactants matters. Math is then used to calculate a rate constant k that produces a linear graph of the concentration vs rate graph.

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