CBSE Class 12 Chemistry Chemical Kinetics Questions Answers

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CHEMICAL KINETICS

1. What do you understand by the rate determining step of a reaction?

2. Find the molecularity of following reaction. RCOOR’ + H₂O --------^H+→RCOOH + R’OH

3. The rate constant of a reaction is 5.0 X 10^-5 L mol^-1 min^-1. What is the order of the reaction?

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

5. What is the order of reaction whose rate constant has the same units as the rate of reaction?

6. Write Arrhenius equation.

7. Define rate constant or specific reaction rate.

8. The reaction A + 3B ----→ 2C obeys the rate equation. Rate = k [A]^1/2 [B]^3/2.What is the order of this reaction? 

9. What are the units of rate constant for a first order reaction?

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

11. What do you understand by half-life period of a reaction?

12. Hydrolysis of ethyl acetate with NaOH is a reaction of second order while with HCl, it is of first order. Why?

13. What is the effect of adding catalyst on the free energy (ΔG) change of a reaction?

14. The rate of a reaction whose rate law is Rate = k [B]ⁿ becomes double on doubling the concentration of B. Find the value n.

15. A reaction is 50% complete in 2 hrs. And 75% complete in 4 hrs. What is the order of reaction?

16. Give one example of a first order reaction.

17. Define threshold energy.

18. The reaction A+B --→ C has zero order. What is the rate equation?

19. Which reactions proceed with constant rate?.

20. How does catalyst affect rate of reaction?

21. . For a chemical reaction represented by R→ P the rate of reaction is denoted by –d [R]/dt or +d[P]/dt . State the significance of plus and minus sign.

22. Express the rate of reaction in terms of disappearance of hydrogen andappearance of ammonia in the given reaction. N₂(g) + 3 H₂ (g) → 2NH₃ (g)

23. Why rate of reaction does not remain constant throughout?

24. Write the unit of first order rate constant of a gaseous reaction if the partial pressure of gaseous reactant is given in bar.

25. What will be the order of reaction, if the rate of reaction does not depend on the concentration of any of the reactant?

26. For the elementary step of a chemical reaction :H₂ + I₂ →2HI rate of reaction →[H₂] [I₂]What is the (i) molecularity and (ii) order of the reaction.

27. For a chemical reaction A→ B. The rate of the reaction is given as Rate =k [A]ⁿ the rate of the above reaction quadruples when the concentration of A is doubled. What is the value of n?

28. Mention one example of zero order reaction.

29. What is the value of the order of reaction of radioactive decay?

30. Express the relation between the half life period of a reactant and initial concentration for a reaction of nth order.

31. A reaction is 50% complete in 2 hours and 75% complete in 4 hours. What is the order of reaction?  

32. Suggest an appropriate reason for the observation : “On increasing temperature of the reacting system by 10 degrees, the rate of reaction almost doubles or even sometimes becomes five folds.”

33. For a chemical reaction, activation energy is zero and at 300K rate constant is 5.9 × 10^-5s^–1, what will be the rate constant at 400K?

34. Two reactions occuring at the same temperature have identical values of Ea. Does this ensure that also they will have the same rate constant? Explain.

35. The rate constant of a reaction is given by the expression k = Ae–Ea/RT. Which factor in this expression should register a decrease so that the reaction proceeds rapidly?

36. For a chemical reaction rate constant k = 5.3 × 10^-4mol L–1 s–1, what will be the order of reaction?

37. Write the rate law and order for the following reaction :

AB₂ + C₂→AB₂C + C (slow)

AB₂ + C→AB₂C (Fast)]

38. The conversion of molecules X to Y follows second order kinetics. If concentration of X is increased to 3 times how will it affect the rate of formation of Y.

39. When rate of reaction becomes equal to specific reaction rate.

40. 87.5% of the substance disintegrated in 45 minutes (first order reaction) .What is its Half life.

ANSWERS 

1. The slowest step in a reaction is known as rate determining step.

2. Molecularity of reaction = 2 (there are two reactant molecules in balanced equation)

3. The order of reaction is 2.

4. Rate of reaction depends upon concentration of reactants which keep on decreasing with time. Hence, rate of reaction does not remain constant throughout.

5. Zero order.

6. Ae-Ea/RT Where,k = Rate constant Ea = Activation energy A = Arrhenius factor

7. When the molar concentration of each reactant is unity, the rate of reaction is called specific

reaction rate.

8. Order =(1/2) + (3/2) = 2

9. s-1

10. For elementary reaction, order and molecularity are same. These reactions are carried out. 

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