U4 Chemical Kinetics_LP 1 to 12_2023_24.pptx

Chemical kinetics

1. Chemical Kinetics Session Type:  Virtual ​ Session No:  1​/12 Session Duration:  35 minutes​

2. This session includes Sub units Meaning and scope of chemical kinetics, Rate of reaction Objectives Students should know The definition of chemical kinetics, rate of chemical reaction, concept of slow and fast reaction- explanation in terms of bonds , Rate of reaction and its units

3. Chemical Kinetics The branch of chemistry which deals with the study of reaction rates and the mechanism by which they occur is called Chemical Kinetics . Scope and importance Studies path Studies kinetics Rate of reaction Mechanism of reaction

4. Rate of reaction Change in concentration of any of the reactants or any of the products per unit time

5. Chemical Kinetics Session Type:  Virtual ​ Session No:  2​/12 Session Duration:  35 minutes​

6. This session includes Sub units Average and instantaneous rate of reaction Objectives Students should know Average and Instantaneous rate of reaction, graphical determination of rate of reaction and simple problems on rate of reaction

7. Average rate of reaction Change in concentration of any of the reactants of any of the products per unit time over a specified interval of time is called the average rate of the reaction

8. Instantaneous Rate of reaction The rate of change of concentration of any of the reactants or products at a particular instant of time is called the instantaneous rate of the given reaction at that instant of time.

9. Pg 207 Ex 4.2

10. Pg 267: Ex. 4.8

11. Chemical Kinetics Session Type:  Virtual ​ Session No:  3​/12 Session Duration:  35 minutes​

12. This session includes Sub units Law of mass action and rate law Objectives Students should know Factors affecting the rate of reaction, Law of mass action and concept of active mass.

13. What is average and instantaneous rate of reaction?

14. Factors affecting rate of reaction Surface area Nature of reactants Concentration Temperature Radiation Catalyst

15. 1. Surface area Rate of reaction increases with surface area Finely divided react fast Powdered coke vs lump of coal

16. 2. Nature of reactants Rearrangement of atoms Ionic/ polar: fast ( aq ) Covalent: slow 2NO + O 2  2NO 2 (Fast) 2CO + O 2  2CO 2 (slow)

17. 3. Concentration of reactants Rate increases with concentration More collisions

18. 4 and 5. Temperature and radiation Rate increases with temp and radiation For homologous reactions rate doubles per 10 rise

19. 6: Catalyst Rate increases with catalyst Does not take part in reaction Forms complex with reactants

20. Law of mass action At constant temperature the rate of a chemical reaction is directly proportional to the product of active masses of reacting species, with each active mass term raised to the power equal to the stoichiometric coefficient of that species in the chemical reaction.

21. Active mass Concentration unit [A] Partial Pressure unit

22. Chemical Kinetics Session Type:  Virtual ​ Session No:  4​/12 Session Duration:  35 minutes​

23. This session includes Sub units Effect of concentration of reactants on rate Objectives Students should know Dependence of rate of reaction on concentration of reactants, Rate law, rate constant

24. Rate law The mathematic expression which describes the experimentally observed dependence of the reaction rate on the molar concentrations of the reactants. The power may or may not be equal to the stoichiometric coeff . Rate = k (concentration of reactants) n

25. Examples

26. Rate constant and its units Rate constant is equal to the rate of reaction when the concentration of the reactant is unity

27. Chemical Kinetics Session Type:  Virtual ​ Session No:  5/12 Session Duration:  35 minutes​

28. This session includes Sub units Order of reaction Objectives Students should know Calculation of order of a reaction from the rate law, units of rate constant, Rate equation for Zero order and first order reaction , Mathematical derivation of rate equation for first order reactions

29. Order of reaction The power to which the concentration term of a particular reactant in the rate law is raised is called the order of reaction with respect to that reactant and the sum of all the powers to which the concentration terms in the rate la are raised to express the observed rate of reaction is called overall rate of reaction. Rate = k [A] p [B] q [C] r Overall order of reaction = p + q + r

30. Order of reaction: Purely experimental Usually whole no. But zero, fraction and negative value possible

31. Zero order and First order Rate = k [A] Independent of reactant conc. Remains constant throughout

32. First order (mathematical)

33. HW: Q. No 20, 22 page no. 252

34. Chemical Kinetics Session Type:  Virtual ​ Session No:  6/12 Session Duration:  35 minutes​

35. This session includes Sub units Half life period Objectives Students should know Half-life period- its definition, mathematical expression, simple problems on first order rate equation and half life period

36. Characteristics of first order reaction Rate directly proportional to conc. of reactant Units: rate = time-1 and for k = s-1, mol-1, hour-1 etc Follows eq. 4.20 Plot of log10[A] against t is always straight line slope = -k/2.303 Half life is independent of initial conc. Time taken for completion is independent of initial conc.

37. Half life period Time taken for half of the reaction to get completed

38. Half life periods depends only on rate constant Independent of initial conc. Amount of reactant left after ‘n’ half lives = [A ]/2 n

39. Chemical Kinetics Session Type:  Virtual ​ Session No:  7/12 Session Duration:  35 minutes​

40. This session includes Sub units Molecularity of reaction Objectives Students should know Molecularity of a reaction – its definition, relation between order , molecularity and the rate of reaction. Students should be able to understand the difference between order and molecularity of a reaction.

41. Molecularity of reaction It is the number of reacting species (atoms, ions or molecules) which must collide simultaneously in order to bring about a chemical reaction.

42. relation between order, molecularity and rate of reaction

43. Chemical Kinetics Session Type:  Virtual ​ Session No:  8​/12 Session Duration:  35 minutes​

44. This session includes Sub units The concept of energy - exothermic and endothermic reaction Objectives Students should know the definition of exothermic and endothermic reaction , concept of energy barrier, threshold and activation energy, formation of activated complex , effect of catalyst on activation energy and reaction rate.

45. Exothermic The chemical reaction proceeds with evolution of heat energy H reactants > H products ΔH = - ve Endothermic The chemical reaction proceeds with absorption of heat energy H reactants < H products ΔH = + ve

46. Energy barrier All collisions are not successful Until molecules have minimum energy called threshold energy Ea = E Threshold - E reactants

47. Activation energy and activation complex It is the excess energy that the reactant molecules (having energy less than the threshold energy) must acquire in order to cross the energy barrier and to change into products. The intermediate configuration corresponding to the maximum potential energy of the system is called activated complex or transition state

48. Effect of catalyst on activation energy and reaction rate

49. What is threshold energy and how it is related to the activation energy of the reaction? HOMEWORK

50. Chemical Kinetics Session Type:  Virtual ​ Session No:  9​/12 Session Duration:  35 minutes​

51. This session includes Sub units Collision theory Objectives Students should know The conditions required for a chemical change to occur and for effective collision – optimum energy and proper orientation during collision, energy barrier, difference in energy of the reactant and the product- exothermic and endothermic reaction with graphs

52. What is your observation?

53. Salient features: Collison theory Reaction occurs only after collision All collisions are not effective Collisions are effective only when Threshold energy

54. Conditions required for effective collision Energy barrier > or = Threshold energy Orientation barrier

55. Increase in temperature Increase in temperature increase the number of effective collisions resulting in increase in rate of reaction

56. Page 254- Q. 39 HOMEWORK

57. Chemical Kinetics Session Type:  Virtual ​ Session No:  10​/12 Session Duration:  35 minutes​

58. This session includes Sub units Mechanism of the reaction Objectives Students should know the concept of elementary reaction, complex reaction and overall reaction, explanation of the mechanism of the reaction, slowest step of the reaction, relation between the rate expression, order of reactants and products at the rate determining step, unit of rate constant

59. Elementary and Complex reaction

60. Mechanism of reaction A sequence of intermediate steps or elementary processes proposed to account for the overall stoichiometry of a reaction is called mechanism of the reaction. Elementary reactions Complex reactions

61. Rate determining step Slowest step decides rate of reaction

62. Relationship between the rate expression, order of reactants products at the rate-determining step, units of rate constant

63. What do you understand by the mechanism of a reaction?

64. Chemical Kinetics Session Type:  Virtual ​ Session No:  1​1/12 Session Duration:  35 minutes​

65. This session includes Sub units Effect of temperature on rate constant of a reaction Objectives Students should know Arrheniusequation Meaning of the symbols of Arrhenius equation and the related graph, evaluation of E a & A from the graph,relationship between the increase in temperature and the number of collisions.

66. Who am I?

67. Arrhenius equation

68. Graphical

69. Chemical Kinetics Session Type:  Virtual ​ Session No:  12​/12 Session Duration:  35 minutes​

70. This session includes Sub units Numerical problems based on Arrhenius equation Objectives Students should be able to solve the numerical problems based on Arrhenius equation

71. e.g. 4.26 , e.g. 4.28, eg. , 4.29 on page no 271

72. Q.No . 4.30 from page 272