Why do we always use coefficients for equilibrium constant equations?

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Nov 6, 2019
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For my understanding, with the exception of all the steps of the reaction given, including the rate-determining (slowest) step, that would determine the rate law reaction, the rate law reaction (order of each reactant and the overall reaction order) must be determined experimentally. For an equilibrium constant, the coefficients for the overall formula for the reverse and forward reactions, can be used to put together the equilibrium constant formula?

Is the reason one can use the coefficients in equilibrium constant equation because one is using the equilibrium overall reaction and at equilibrium there will be equal amounts of product and reactants versus rate law equations, where you don't know where equilibrium is and you don't know which steps will be the slowest, unless given? From what I read, the equilibrium constant can be derived from the forward and reverse rate reaction equations (since these reactions are going in the forward and reverse directions, where in rate law reactions, irreversible reactions are almost always used, unless otherwise stated, and a rate law is designed for the forward and reverse direction, hence, why, I think we only use the reactants in rate law equations? ), but within the equilibrium constant equation, one can use the coefficients. Could someone explain why you can always use coefficients for the equilibrium constant equation?