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: Understanding the Concept
Order is the sum of the powers of concentrations in the rate law. Molecularity is the number of reacting molecules colliding in an elementary step.

Step 2: Order
The rate is \(k[\text{NO}_2]^2\), so the order is 2 (second order).

Step 3: Molecularity
The reaction is stated to be elementary. Two \(\text{NO}_2\) molecules collide, so the molecularity is 2. A reaction with molecularity two is called bimolecular (the option spells it "biomolecular").

Step 4: Check the options
(B) says first order, which is wrong because the power is 2. (C) says unimolecular, which is wrong because two molecules take part. (D) gives zero order, which is wrong. Only (A) has second order and bimolecular.

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