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Assertion (A) Order of the reaction can be zero or fractional.

Reason (R) We cannot determine order from balanced chemical equation.

(a) Both assertion and reason are correct and the reason is correct explanation of assertion
(b) Both assertion and reason are correct, but reason does not explain assertion.
(c) Assertion is correct, but reason is incorrect
(d) Both assertion and reason are incorrect
(e) Assertion is incorrect but reason is correct.

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Answer (b). Both assertion and reason are correct, but the reason is not the correct.

The order of reaction can be defined as the power dependence of rate on the concentration of all reactants. For example, the rate of a first-order reaction is dependent solely on the concentration of one species in the reaction. Some characteristics of the reaction order for a chemical reaction are listed below.

  • Reaction order represents the number of species whose concentration directly affects the rate of reaction.
  • It can be obtained by adding all the exponents of the concentration terms in the rate expression.
  • The order of reaction does not depend on the stoichiometric coefficients corresponding to each species in the balanced reaction.
  • The reaction order of a chemical reaction is always defined with the help of reactant concentrations and not with product concentrations.
  • The value of the order of reaction can be in the form of an integer or a fraction. It can even have a value of zero.

In order to determine the reaction order, the power-law form of the rate equation is generally used. The expression of this form of the rate law is given by r = k [A]x[B]y

In the expression described above, ‘r’ refers to the rate of reaction, ‘k’ is the rate constant of the reaction, [A] and [B] are the concentrations of the reactants. The exponents of the reactant concentrations x and y are referred to as partial orders of the reaction. Therefore, the sum of all the partial orders of the reaction yields the overall order of the reaction.

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