1. IGCSE CHEMISTRY SECTION 4 LESSON 3

2. Content The iGCSE Chemistry course Section 1 Principles of Chemistry Section 2 Chemistry of the Elements Section 3 Organic Chemistry Section 4 Physical Chemistry Section 5 Chemistry in Society

3. Content Section 4 Physical Chemistry a)Acids, alkalis and salts b)Energetics c)Rates of reaction d)Equilibria

4. Lesson 3 c) Rates of reaction 4.17 describe experiments to investigate the effects of changes in surface area of a solid, concentration of solutions, temperature and the use of a catalyst on the rate of a reaction 4.18 describe the effects of changes in surface area of a solid, concentration of solutions, pressure of gases, temperature and the use of a catalyst on the rate of a reaction 4.19 understand the term activation energy and represent it on a reaction profile 4.20 explain the effects of changes in surface area of a solid, concentration of solutions, pressure of gases and temperature on the rate of a reaction in terms of particle collision theory 4.21 explain that a catalyst speeds up a reaction by providing an alternative pathway with lower activation energy.

5. Rates of Reaction The rate of reaction is the rate at which products are formed, or the rate at which reactions are used up, in a reaction.

6. Rates of Reaction Chemical reactions will only occur when the reacting particles collide with each other with sufficient energy so they react.

7. Rates of Reaction Chemical reactions will only occur when the reacting particles collide with each other with sufficient energy so they react. The ACTIVATION ENERGY is the minimum amount of energy required to cause the reaction to happen.

8. Rates of Reaction Chemical reactions will only occur when the reacting particles collide with each other with sufficient energy so they react. The ACTIVATION ENERGY is the minimum amount of energy required to cause the reaction to happen. There are FIVE very important factors which can affect the rate of reaction.

9. Rates of Reaction Temperature

10. Rates of Reaction Temperature Pressure (of gases)

11. Rates of Reaction Temperature Pressure (of gases) Concentration

12. Rates of Reaction Temperature Pressure (of gases) ConcentrationSurface Area

13. Rates of Reaction Temperature Pressure (of gases) ConcentrationSurface AreaCatalysts

14. Rates of Reaction Temperature Pressure (of gases) ConcentrationSurface AreaCatalysts Let’s not forget here a little dose of kinetic theory

15. Rates of Reaction Temperature Pressure (of gases) ConcentrationSurface AreaCatalysts Let’s not forget here a little dose of kinetic theory Kinetic what?

16. Rates of Reaction Kinetic theory is all about the random movement of particles

17. Rates of Reaction Kinetic theory is all about the random movement of particles

18. Rates of Reaction Kinetic theory is all about the random movement of particles Kinetic theory assumes that particles are in constant random motion

19. Rates of Reaction Kinetic theory is all about the random movement of particles Kinetic theory assumes that particles are in constant random motion ! And there will be collisions!

20. Rates of Reaction Kinetic theory is all about the random movement of particles Kinetic theory assumes that particles are in constant random motion ! And there will be collisions! It’s these collisions that are the cause of chemical reactions.

21. Rates of Reaction Do you remember the five factors that can affect the rate of chemical reactions?

22. Rates of Reaction

23. Let’s now consider each one of these factors in turn

24. Rates of Reaction 1. Temperature of the Reactants

25. Rates of Reaction 1. Temperature of the Reactants Cold conditions, particles have little energy, move slowly and collide infrequently and less successfully Low temperature

26. Rates of Reaction 1. Temperature of the Reactants Cold conditions, particles have little energy, move slowly and collide infrequently and less successfully HEAT When heated, particles have more energy, move faster, collide frequently and more successfully Low temperature High temperature

27. Rates of Reaction 1. Temperature of the Reactants Cold conditions, particles have little energy, move slowly and collide infrequently and less successfully HEAT When heated, particles have more energy, move faster, collide frequently and more successfully Low temperature High temperature Raising the temperature = particles move faster and collide frequently, collisions are successful and so the rate of reaction increases !

28. Rates of Reaction 2. Concentration of the Dissolved Reactants

29. Rates of Reaction 2. Concentration of the Dissolved Reactants Low concentration Particles are spread out and will collide with each other less often, with fewer successful collisions

30. Rates of Reaction 2. Concentration of the Dissolved Reactants Low concentration Particles are spread out and will collide with each other less often, with fewer successful collisions Particles are crowded close together, so collide more often, with more successful collisions High concentration

31. Rates of Reaction 2. Concentration of the Dissolved Reactants Low concentration Particles are spread out and will collide with each other less often, with fewer successful collisions Particles are crowded close together, so collide more often, with more successful collisions High concentration Increasing the concentration = particles are more crowded together and collide frequently, collisions are successful and so the rate of reaction increases !

32. Rates of Reaction 3. Pressure (in gases)

33. Rates of Reaction 3. Pressure (in gases) Low pressure Particles are spread out and will collide with each other less often, with fewer successful collisions

34. Rates of Reaction 3. Pressure (in gases) Low pressure Particles are spread out and will collide with each other less often, with fewer successful collisions High pressure Particles are pushed closer together, they collide more frequently, with more successful collisions

35. Rates of Reaction 3. Pressure (in gases) Low pressure Particles are spread out and will collide with each other less often, with fewer successful collisions High pressure Particles are pushed closer together, they collide more frequently, with more successful collisions Increasing the pressure = particles in a gas are pushed closer together and collide frequently, collisions are successful and so the rate of reaction increases !

36. Rates of Reaction 4. Surface area of solid reactants

37. Rates of Reaction 4. Surface area of solid reactants Small surface area Large particles have a small surface area in relation to volume – less particles exposed, fewer collisions, slow reaction

38. Rates of Reaction 4. Surface area of solid reactants Small surface area Large particles have a small surface area in relation to volume – less particles exposed, fewer collisions, slow reaction Large surface area Smaller particles have a larger surface area in relation to volume- more particles exposed, more collisions, faster reaction

39. Rates of Reaction 4. Surface area of solid reactants Small surface area Large particles have a small surface area in relation to volume – less particles exposed, fewer collisions, slow reaction Large surface area Smaller particles have a larger surface area in relation to volume- more particles exposed, more collisions, faster reaction Reducing the particle size and so increasing the relative surface area means that there are more successful collisions and a faster rate of reaction.

40. Rates of Reaction 5. Using a catalyst

41. Rates of Reaction 5. Using a catalyst A catalyst is a substance which increases the rate of a chemical reaction without being used up itself. It can be used over and over again.

42. Rates of Reaction 5. Using a catalyst A catalyst is a substance which increases the rate of a chemical reaction without being used up itself. It can be used over and over again.

43. Rates of Reaction 5. Using a catalyst A catalyst is a substance which increases the rate of a chemical reaction without being used up itself. It can be used over and over again. A catalyst lowers the activation energy – the amount of energy needed for a successful collision. There are more collisions, and so a faster reaction.

44. Activation energy What’s all this ‘ere talk about the ACTIVATION ENERGY?

45. Activation energy What’s all this ‘ere talk about the ACTIVATION ENERGY? The ACTIVATION ENERGY is the relatively small amount of energy needed to start a chemical reaction

46. Increasing energy reactants products Time Activation energy Used to break apart the old bonds

47. Increasing energy reactants products Time Activation energy Activation energy using a catalyst. Catalysts reduce the activation energy for the reaction – this makes the reaction go faster.

48. Rate of reaction experiments

49. 1. Surface area Boiling tube Bubbles of hydrogen Magnesium ribbon Hydrochloric acid Time taken for magnesium to disappear = 109 secs

50. Rate of reaction experiments 1. Surface area Boiling tube Bubbles of hydrogen Magnesium ribbon Hydrochloric acid Time taken for magnesium to disappear = 109 secs Time taken for magnesium to disappear = 55 secs Small pieces of Magnesium ribbon

51. Rate of reaction experiments 1. Surface area Boiling tube Bubbles of hydrogen Magnesium ribbon Hydrochloric acid Time taken for magnesium to disappear = 109 secs Time taken for magnesium to disappear = 55 secs Small pieces of Magnesium ribbon Increasing the surface area of reactants increases the rate of reaction

52. Rate of reaction experiments 2. Concentration X 10cm 3 sodium thiosulphate + 40cm 3 water + 10cm 3 hydrochloric acid View from above Volume of sodium thiosulphate (cm 3 ) Volume of water (cm 3 ) 1040 2030 20 4010 500

53. Rate of reaction experiments 2. Concentration 10cm 3 sodium thiosulphate + 40cm 3 water + 10cm 3 hydrochloric acid View from above Volume of sodium thiosulphate (cm 3 ) Volume of water (cm 3 ) Time for cross to disappear (secs) 104098 203064 302031 401016 5008

54. Rate of reaction experiments 2. Concentration 10cm 3 sodium thiosulphate + 40cm 3 water + 10cm 3 hydrochloric acid View from above Volume of sodium thiosulphate (cm 3 ) Volume of water (cm 3 ) Time for cross to disappear (secs) 104098 203064 302031 401016 5008 Volume of thiosulphate Time for cross to disappear

55. Rate of reaction experiments 2. Concentration 10cm 3 sodium thiosulphate + 40cm 3 water + 10cm 3 hydrochloric acid View from above Volume of sodium thiosulphate (cm 3 ) Volume of water (cm 3 ) Time for cross to disappear (secs) 104098 203064 302031 401016 5008 Volume of thiosulphate Time for cross to disappear As the concentration of sodium thiosulphate increases, so the time taken decreases – the rate of reaction gets faster.

56. Rate of reaction experiments 3. Temperature Temperature of reaction mixture ( o C) Reaction time (secs) Average reaction time (secs) Experiment 1Experiment 2Experiment 3 402425 502220 21 601716 701211 807787

57. Rate of reaction experiments 3. Temperature Temperature of reaction mixture ( o C) Reaction time (secs) Average reaction time (secs) Experiment 1Experiment 2Experiment 3 402425 502220 21 601716 701211 807787

58. Rate of reaction experiments 3. Temperature Temperature of reaction mixture ( o C) Reaction time (secs) Average reaction time (secs) Experiment 1Experiment 2Experiment 3 402425 502220 21 601716 701211 807787 As the temperature increases so the time taken for the cross to disappear decreases – the reaction gets faster.

59. Rate of reaction experiments 4. Catalysts Hydrogen peroxide Manganese oxide catalyst 2H 2 O 2  2H 2 O + O 2 Decomposition of hydrogen peroxide The rate of reaction is measured by how long it takes for the gas to be produced.

60. Rate of reaction experiments 4. Catalysts Hydrogen peroxide Manganese oxide catalyst 2H 2 O 2  2H 2 O + O 2 Decomposition of hydrogen peroxide Volume of gas produced (cm 3 ) 100 80 60 40 20 0 0 10 20 30 40 50 60 70 80 90 100 Time (secs) 1 2 3

61. Rate of reaction experiments 4. Catalysts Hydrogen peroxide Manganese oxide catalyst 2H 2 O 2  2H 2 O + O 2 Decomposition of hydrogen peroxide Volume of gas produced (cm 3 ) 100 80 60 40 20 0 0 10 20 30 40 50 60 70 80 90 100 Time (secs) 1 2 3 Better catalysts give a quicker reaction as shown by the steeper graph

62. Rate of reaction experiments 4. Catalysts Hydrogen peroxide Manganese oxide catalyst 2H 2 O 2  2H 2 O + O 2 The catalyst manganese oxide increases the rate of decomposition of hydrogen peroxide. Volume of gas produced (cm 3 ) 100 80 60 40 20 0 0 10 20 30 40 50 60 70 80 90 100 Time (secs) 1 2 3 Better catalysts give a quicker reaction as shown by the steeper graph

63. End of Section 4 Lesson 3 In this lesson we have covered: Rates of Reaction Activation Energy Rates of Reaction Experiments