NVAEasyJEE 2023Order & Molecularity

JEE Chemistry 2023 Question with Solution

For conversion of compound AA \rightarrow BB, the rate constant of the reaction was found to be 4.6×105L mol1s14.6 \times 10^{-5} \, \text{L mol}^{-1} \, \text{s}^{-1}. The order of the reaction is _____

Answer

Correct answer:2

Step-by-step solution

Standard Method

Given: For conversion of compound AA \rightarrow BB, the rate constant is 4.6×105L mol1s14.6 \times 10^{-5} \, \text{L mol}^{-1} \, \text{s}^{-1}.

Find: The order of the reaction.

The unit of the rate constant is given as Lmol1s1\text{L} \, \text{mol}^{-1} \, \text{s}^{-1}, which corresponds to a second-order reaction. The general formula for the unit of a rate constant is:

Unit of k=(concentration)1n×time1\text{Unit of } k = \text{(concentration)}^{1-n} \times \text{time}^{-1}

where nn is the order of the reaction. For n=2n = 2, the unit becomes Lmol1s1\text{L} \, \text{mol}^{-1} \, \text{s}^{-1}.

Therefore, the order of the reaction is 22.

Common mistakes

  • Confusing the unit of the rate with the unit of the rate constant is a common mistake. The order is identified from the unit of kk, not from the unit of reaction rate. Always compare the given unit with the general unit expression for kk.

  • Using the wrong relation between order and units can lead to an incorrect answer. The unit of kk is (concentration)1n×time1(\text{concentration})^{1-n} \times \text{time}^{-1}, so the exponent 1n1-n must be matched carefully with the concentration term.

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