Question

The order for the given reaction is :
\( \text{A} + 2\text{B} \rightarrow \text{Products} \)
\( \text{Rate} = k[\text{A}]^{1/2} [\text{B}]^1 \)

• A. \( 1.5 \)
• B. \( 1 \)
• C. \( 0.5 \)
• D. \( 2 \)

Hint:

Never use the coefficients from the balanced equation (like the '2' in 2B) to determine the order unless you are explicitly told the reaction is "elementary". Always use the exponents given in the Rate Law.

Answer 1

The Correct Option is A

Step 1: What the order of a reaction means.
The overall order of a reaction is simply the sum of the powers to which the concentration terms are raised in the experimentally found rate law, and this sum does not have to match the stoichiometric coefficients of the balanced equation at all.
Step 2: Reading off the powers from the given rate law.
We are told \[ \text{Rate} = k[A]^{1/2}[B]^{1} \] so the power on $A$ is $\tfrac{1}{2}$, meaning the reaction is half order in $A$, and the power on $B$ is $1$, meaning it is first order in $B$.
Step 3: Adding the powers together. \[ n = \frac{1}{2} + 1 = 1.5 \]
Step 4: What this fractional value tells us.
A non-integer overall order like $1.5$ is a strong sign that this reaction does not happen in one single collision step, it proceeds through a multi-step mechanism whose slowest step decides this observed rate law. \[ \boxed{1.5} \]