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MHT CET202527 Apr 2025Evening ShiftChemistryChemical KineticsActual

What is numerical value of rate constant of a first order reaction that is 20 % completed in 10 minute ?

Options

  1. A0.0223
  2. B0.0322
  3. C0.223
  4. D0.322

Correct answer

A. 0.0223

Step-by-step solution

The integrated rate law for a first-order reaction is k = 2.303 t ( [A]₀ [A]_t ) . Since the reaction is 20% complete after 10 minutes, [A]_t = 0.8[A]₀ . Choosing [A]₀ = 100 and [A]_t = 80 gives [A]₀ [A]_t = 1.25 . k = 2.303 10 (1.25) 0.2303 0.0969 0.02231 min ⁻¹ This matches option A .

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