Question

In the reaction, A \( \rightarrow \) products, if the concentration of the reactant is doubled but the rate of reaction remains unchanged, what is the order of the reaction with respect to A?

• A. 1
• B. 2
• C. 0.5
• D. 0

Hint:

In a zero-order reaction, the rate is independent of the concentration of reactants.

Answer 1

The Correct Option is D

Step 1: Understanding the Rate Law 
The general rate law is: \[ r = k[A]^n \] where \( n \) is the order of the reaction. 
Step 2: Given Condition 
When the concentration of \( A \) is doubled, the rate remains unchanged. 
Mathematically, \[ r_2 = k[2A]^n \] Since \( r_1 = r_2 \), we equate: \[ k[A]^n = k[2A]^n \] 
Step 3: Solving for \( n \) 
Dividing both sides: \[ 1 = 2^n \] \[ 2^n = 1 \] \[ n = 0 \] Final Answer: The reaction follows zero order kinetics.

Answer 2

Step 1: Understand the relation between rate and concentration
The order of a reaction with respect to a reactant indicates how the rate changes when the concentration of that reactant changes.

Step 2: Analyze the given situation
Here, when the concentration of A is doubled, the rate of the reaction remains unchanged.
This means the rate does not depend on the concentration of A.

Step 3: Determine the order of reaction
If the rate is independent of the concentration of A, the order of the reaction with respect to A is zero.
Mathematically, rate = k [A]^0 = k, which is constant regardless of [A].

Step 4: Final Conclusion
Therefore, the order of the reaction with respect to A is zero.