NEETChemistryChemical Kinetics
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): For a first-order reaction, the time taken for 99 % completion is exactly twice the time taken for 90 % completion. Reason (R): The time required for the completion of a given fraction of a first-order reaction is independent of its initial concentration. In the light of the above statements, choos
Options
- ABoth (A) and (R) are true and (R) is the correct explanation of (A)
- BBoth (A) and (R) are true but (R) is not the correct explanation of (A)
- C(A) is true but (R) is false
- D(A) is false but (R) is true
Correct answer
B. Both (A) and (R) are true but (R) is not the correct explanation of (A)
Step-by-step solution
For a first-order reaction, the time required for a specific percentage of completion is given by t = 2.303 k ( a₀ a₀ - x ) . For 90 % completion: t_ 90 % = 2.303 k ( 100 100 - 90 ) = 2.303 k (10) = 2.303 k For 99 % completion: t_ 99 % = 2.303 k ( 100 100 - 99 ) = 2.303 k (100) = 2 2.303 k Therefore, t_ 99 % = 2 t_ 90 % . Assertion (A) is true. Reason (R) states that the time for fractional completion is independent of initial concentration, which is a true characteristic of first-order kinetics. However, this fact