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# What is the molecularity of a reversible reaction?

I know that the definition of molecularity of a reaction is number of species reacting in an elementary step. But considering the theory of microscopic reversibility for elementary reactions, each reaction can be assumed to be reversible. In that case, if $$\ce{A <=> B + C}$$ then what is the molecularity of the reaction? Is it 1 or 2?

For the reaction $$\ce {A <=> B + C}$$ its molecularity is unimolecular. If we were given $$\ce{B + C <=> A}$$ Its molecularity would be bimolecular. Thus we see molecularity is dependent on the number of reactant particles, even if it's in equilibrium.

Since the equilibrium constant also changes when we reverse a reaction, so does the molecularity of the reaction.
So many properties of reversible reactions are defined in the way we write down the reaction.

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# What is the molecularity of a reversible reaction?

I know that the definition of molecularity of a reaction is number of species reacting in an elementary step. But considering the theory of microscopic reversibility for elementary reactions, each reaction can be assumed to be reversible. In that case, if $$\ce{A <=> B + C}$$ then what is the molecularity of the reaction? Is it 1 or 2?

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For the reaction $$\ce {A <=> B + C}$$ its molecularity is unimolecular. If we were given $$\ce{B + C <=> A}$$ Its molecularity would be bimolecular. Thus we see molecularity is dependent on the number of reactant particles, even if it's in equilibrium.

Here also the use of the arrows is wrong, see my comment to the question. - Martin - マーチン May 5 '15 at 14:34

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