Bihar Board - Class 12 Chemistry - Chapter 4: Chemical Kinetics Short Answer Question

The short question answers for Chapter 4: Chemical Kinetics of Class 12 Chemistry are provided here in English. These questions are prepared based on the NCERT curriculum for Class 12. They will help students understand the chapter easily. These short question answers will be useful not only for the Class 12 board exams but also for entrance exams like NEET. The questions and answers for Bihar Board Class 12 Chemistry, Chapter 4: Chemical Kinetics, have been prepared by expert teachers at Vidyakul.

Short Questions and Answers

Q. 1. Define the term “order of reaction” for chemical reactions.

Ans⇒ The sum of the exponents (powers) of the concentration of reactant in the rate law is termed as order of the reaction. It can be in fraction and can be zero also.

Q. 2. How does the value of rate constant vary with reactant concentration?

Ans⇒ For a particular reaction at a particular temperature, rate constant is constant and does not depend upon concentrations of the reactants.

Q. 3. Distinguish between ‘rate expression’ and ‘rate constant of a reaction.

Ans⇒ Rate of reaction is defined as change in concentration of reactants or products per unit time. Its unit is mol.

Q. 4. Define threshold energy of a reaction.

Ans⇒ Threshold energy is the minimum energy which must be possessed by reacting molecules in order to undergo effective collision which leads to formation of product molecules.

Q. 5. Write expression for half-life in case of a reaction between hydrogen and chlorine to form hydrochloric gas.

Ans⇒ Given reaction is zero order reaction. Hence .

Q. 6. If the half-life period of a reaction is inversely proportional to initial concentration of a reactant, what is the order of the reaction?

Ans⇒ Two, this is because for order reactions.

Q. 7. For a reaction, the rate of the reaction can be denoted by or . State the significance of plus and minus signs in this case.

Ans ⇒ Minus sign indicates the decrease in the concentration of the reactant while plus sign indicates an increase in the concentration of the product with time.

Q. 8. Why does the rate of reaction not remain constant throughout?

Ans⇒ Because it depends upon concentration of the reactions which keeps on decreasing with time.

Q. 9. What is the relationship between rate constant and activation energy of a reaction?

Ans⇒ is the Arrhenius equation.

Q. 10. Why hydrolysis of ethyl acetate with is a second order reaction while with it is a order reaction?

Ans⇒ Rate of hydrolysis of ethyl acetate with depends upon concentration of both while that with , it depends upon only the concentration of ethyl acetate.

Q. 11. Define specific reaction rate or rate constant.

Ans⇒ It is the rate of a reaction when the molar concentration of each of the reactants is unity.

Q. 12. What is the rate determining step of a reaction?

Ans⇒ The slowest step of a multi-step reaction is called its rate determining step.

Q. 13. In some cases, it is found that a large no. of colliding molecules have energy more than threshold energy, yet the reaction is slow, why?

Ans⇒ The colliding molecules may not have proper orientation at the time of collision.

Q. 14. Give an example of a pseudo first order reaction.

Ans⇒ Acid catalyzed hydrolysis of ethyl acetate.

Q. 15. What is meant by an elementary reaction?

Ans⇒ A reaction which takes place in one step P is called an elementary reaction.

Q. 16. How is the half-life period related to initial concentration of a second order reaction?

Ans⇒ Thus half life period of a second order reaction is inversely proportional to the initial concentration of the reactant.

Q. 17. Give one example of a reaction where order and molecularity are equal.

Ans⇒ Order and molecularity are the same in a single step reaction. eg.

Q. 18. State any one condition under which a bimolecular reaction may be kinetically of first order.

Ans⇒ A bimolecular reaction may become kinetically of the first order if one of the reactants is present in excess.

Q. 19. How is the rate constant of a reaction related to the concentration of the reactants?

Ans⇒ Rate constant does not depend upon the concentration of the reactants.

Q. 20. The rate law for the reaction: is . What would be the effect on the rate if (i) concentration of the ester is doubled, (ii) concentration of is it doubled?

Ans⇒ (i) The rate of the reaction will be doubled. (ii) No effect on rate.

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