Question

For the following reaction in alkaline medium:
$OC{{l}^{+}}+{{I}^{-}}\xrightarrow{O{{H}^{-}}}OI+C{{l}^{-}}$, rate law was found to be $r=K[OC{{l}^{-}}][{{I}^{-}}]{{[O{{H}^{-}}]}^{-1}}$, thus order with respect to $O{{H}^{-}}$ ion is:
(A) 1
(B) 1
(C) 3
(D) 2

Answer 1

Hint: The order of the reaction is the sum of the exponents or powers of the molar concentrations in the rate law equation. So, the equation has a rate, $r=k{{[A]}^{a}}{{[B]}^{b}}$, its order will be equal to $a+b$, and the order due to $[A]$ will be a and the order due to $[B]$ will be b.

Complete step by step solution:
Whenever the chemical reaction takes place, the concentration of the products increases and the concentration of the reactants decrease because the reactant is changing into the product.
But when we calculate the rate of reaction of the equation ii is found to decrease. From this, we can conclude that the rate of reaction only depends on the concentration of the reaction.
For example, suppose a reaction is:
$mM+nN\to \text{ Products}$
The rate of the reaction for this will be:
$Rate\propto {{[M]}^{m}}{{[N]}^{n}}$
$Rate=k{{[M]}^{m}}{{[N]}^{n}}$
From this, we can define the order of the reaction also, the order of the reaction is the sum of the exponents or powers of the molar concentrations in the rate law equation. So, the equation has a rate, $Rate=k{{[M]}^{m}}{{[N]}^{n}}$, its order will be equal to$m+n$, and the order due to $[M]$ will be m and the order due to $[N]$ will be n.
So, reaction given is $OC{{l}^{+}}+{{I}^{-}}\xrightarrow{O{{H}^{-}}}OI+C{{l}^{-}}$ and its rate law is given:
$r=K[OC{{l}^{-}}][{{I}^{-}}]{{[O{{H}^{-}}]}^{-1}}$
So the order of the reaction due to $O{{H}^{-}}$ion will be -1 because -1 is the power of the hydroxyl ion.

Therefore, the correct answer is an option (A) 1.

Note: The rate law of the reaction cannot be easily predicted by just looking at the reaction, it is only calculated by experimental verification. The order of the reaction can have any value like zero, negative, positive, or even fraction.