Target Exam

CUET

Subject

Chemistry

Chapter

Physical: Chemical Kinetics

Question:

Statement I: If in a zero-order reaction, the concentration of the reactant is doubled, the half-life period is also doubled

Statement II: For a zero-order reaction, the rate of reaction is independent of the initial concentration

Options:

Statement I and statement II are correct and statement II is the correct explanation of statement I

Statement I and statement II are correct but statement II is not the correct explanation of statement I

Statement I is true but statement II is false

Statement I is false but statement II is correct

Correct Answer:

Statement I and statement II are correct but statement II is not the correct explanation of statement I

Explanation:

The correct answer is option 2. Statement I and statement II are correct but statement II is not the correct explanation of statement I.

Statement 1

For a zero-order reaction, the relationship between the half-life period ($t_{1/2}$) and the initial concentration ($[R]_0$) is given by the formula:

$$t_{1/2} = \frac{[R]_0}{2k}$$
  • Conclusion: Since $t_{1/2}$ is directly proportional to the initial concentration ($t_{1/2} \propto [R]_0$), if the concentration of the reactant is doubled, the half-life period will also be doubled.

  • Statement I is CORRECT.

Statement II

The rate law for a zero-order reaction is expressed as:

$$Rate = k[R]^0 = k$$
  • Conclusion: This shows that the rate of reaction remains constant and is independent of the concentration of the reactants at any given time, including the initial concentration.

  • Statement II is CORRECT.

So,

  • Statement I is about the time required for half the reactant to be consumed ($t_{1/2}$).

  • Statement II is about the speed of the reaction ($Rate$).

While both statements are factually true for zero-order reactions, Statement II is not the reason why Statement I is true. Statement I is a direct consequence of the integrated rate equation for zero order, whereas Statement II describes the nature of the rate itself.

  • Correct Option: Option 2 (Both statements are correct, but Statement II is not the correct explanation of Statement I).