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KVPY2019ChemistryChemical Kinetics

For a first order chemical reaction,

Options

  1. Athe product formation rate is independent of reactant concentration.
  2. Bthe time taken for the completion of half of the reaction t 1 / 2 is 69 . 3 % of the rate constant k
  3. Cthe dimension of Arrhenius pre-exponential factor is reciprocal of time.
  4. Dthe concentration vs time plot for the reactant should be linear with a negative slope

Correct answer

C. the dimension of Arrhenius pre-exponential factor is reciprocal of time.

Step-by-step solution

Arrhenius equation for rate constant, k is k = Ae - E a / RT , where A is the pre-exponential factor. Since, e - E a / RT is dimensionless, dimension of A = k . For first order reaction, dimension of k = time - 1 ∴ Also same for A . As for the other options, For a first order reaction, the product formation rate is directly proportional to reactant concentration, half-life = 0 . 693 k or 69 . 3 % of 1 k , and concentration of reactant changes with time by the equation A t = A 0 e - kt , which shows exponentia

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