Consider the elementary step where M is a solvent molecule present in large excess…

CHEMISTRY · Single correct · A Level · Chemistry · Rate equations · Rate equations

Problem

Consider the elementary step A+B+M⟶AB+M\text{A}+\text{B}+\text{M}\longrightarrow\text{AB}+\text{M} where M is a solvent molecule present in large excess and appears unchanged on both sides of the equation. Which statement about this step is most accurate? (a) The step is termolecular; because [M] is effectively constant, the rate can be written as rate = k′[A][B]k'[\text{A}][\text{B}]. (b) The step is termolecular, and the rate law is rate = k[A][B][M]k[\text{A}][\text{B}][\text{M}]. (c) The step is bimolecular, and the rate law is rate = k[A][B]k[\text{A}][\text{B}]. (d) The step is unimolecular, and the rate law is rate = k[A]k[\text{A}].

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