Question

What is the order and molecularity of the following elementary reaction?
\(2\text{NO}_{2(g)}\rightarrow 2\text{NO}_{(g)}+\text{O}_{2(g)}\), rate \(= k\times [\text{NO}_2]^2\)

• A. The reaction is second order and biomolecular.
• B. The reaction is first order and bimolecular.
• C. The reaction is second order and unimolecular.
• D. The reaction is zero order and unimolecular.

Hint:

For an elementary step, molecularity is the number of molecules colliding; order is the sum of powers in the rate law.

Answer 1

The Correct Option is A

Step 1: Approach
Read order from the rate expression and molecularity from the balanced elementary step.

Step 2: Reading
Rate $= k[\text{NO}_2]^2$ has the exponent $2$, so the order is $2$.
The step has the coefficient 2 on $\text{NO}_2$, so two molecules must meet. For an elementary reaction the molecularity equals the sum of the coefficients of the reactants, which is $2$.

Step 3: Result
Both numbers are 2, so the reaction is second order and bimolecular, option (A).

Final Answer:
The reaction is second order and bimolecular, option (A). \[ \boxed{\text{Second order, bimolecular}} \]