Chemical KineticsmediumMCQ SINGLE

A complex chemical reaction follows the rate law . If the concentration of reactant is kept constantChemical Kinetics Chemistry Question

Question

A complex chemical reaction follows the rate law $r = k[A]^x [B]^y$. If the concentration of reactant $A$ is kept constant and reactant $B$ is intentionally taken in very large stoichiometric excess (Ostwald isolation method), the apparent (pseudo) order of the reaction determined experimentally under these specific conditions will be:

Answer: C

💡 Solution & Explanation

When reactant $B$ is in large excess, its concentration remains practically unchanged during the reaction. The term $[B]^y$ becomes a constant and merges with the true rate constant $k$ to form a pseudo rate constant $k' = k[B]^y$. The new rate law becomes $r = k'[A]^x$. The experimentally observed order will be just $x$.

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