Question

The rate of a reaction is doubled when the concentration of the reactant is doubled. The order of the reaction is :

• A. 0
• B. 1
• C. 2
• D. 0.5

Hint:

Direct, linear proportionality between concentration and reaction rate signifies a first-order reaction ($n=1$).

Answer 1

The Correct Option is B

Step 1: Concept
The rate law establishes the mathematical relationship between the rate of a reaction and the concentration of its reactants: $\text{Rate} = k[\text{Reactant}]^n$.

Step 2: Meaning
The exponent $n$ represents the order of the reaction with respect to that reactant.

Step 3: Analysis
According to the question, if the concentration $[\text{Reactant}]$ is multiplied by 2, the new rate becomes $2 \times \text{Rate}$. Substituting this into the rate law gives $2 \times \text{Rate} = k(2[\text{Reactant}])^n$.

Step 4: Conclusion
Dividing the new rate by the original rate yields $2 = 2^n$. Solving for $n$ gives $n = 1$, indicating a first-order reaction.

Final Answer: (B)