For a reaction rate law expression is : Rate = K A 1 2 B 2 . Can the reaction be an elementary ? Explain.

For a reaction rate law expression is given as Rate = k A 1 2 B 2 . Elementary reactions (A balanced chemical equation never gives us a true picture of how a reaction takes place since rarely a reaction gets completed in one step. The reactions taking place in one step are called elementary reactions). The reaction for which the rate law is given cannot be elementary because for the reaction to be elementary, order with respect to the reactant A can not be fractional. A fractional-order represents a transition state formation and this shows that the given reaction is not being completed in one step.

The rate constant for a first order reaction is 90 s - 1 . How much will it take to reduce the concentration of the reactant to 1 20 th of its initial value?

Given: rate constant k for a first-order reaction = 90 s - 1 Let assume: initial concentration R 0 = x The final concentration R = x 20 , reduce the initial concentration of the reactant to its 1 20 t h Formula: t = 2.303 k l o g R 0 R for first-order reaction = 2.303 k l o g x x 20 = 2.303 k l o g 1 1 20 = 2.303 90 s - 1 l o g 20 = 3 . 3 × 10 - 2 s (approximately) Hence, the required time is 3 . 3 × 10 - 2 s . Concept Insight: If the initial concentration is one then the final concentration is 1 20 .

Find the half-life period of first-order reaction whose rate constant K = 4 . 93 × 10 - 4 S - 1 .

The half-life of a reaction is the time in which the concentration of a reactant is reduced to one half of its initial concentration. It is represented as t 1 2 . For the first-order reaction, t 1 2 = 0 . 693 K Give, rate constant K = 4 . 93 × 10 - 4 S - 1 Substituting in the equation we get: t 1 2 = 0 . 693 4 . 93 × 10 - 4 t 1 2 = 1405 . 6 S

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - Chemical Kinetics>Punjab Board-2018>Q 1

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What are the units of Rate constant for First Order reaction?

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