1. A guide for GCSE students KNOCKHARDY PUBLISHING
RATES OF REACTION
A guide for GCSE students
2010 SPECIFICATIONS
KNOCKHARDY PUBLISHING

2. RATES OF REACTION www.knockhardy.org.uk INTRODUCTION
This Powerpoint show is one of several produced to help students understand selected GCSE Chemistry topics. It is based on the requirements of the AQA specification but is suitable for other examination boards.
Individual students may use the material at home for revision purposes and it can also prove useful for classroom teaching with an interactive white board.
Accompanying notes on this, and the full range of AS and A2 Chemistry topics, are available from the KNOCKHARDY WEBSITE at...
All diagrams and animations in this Powerpoint are original and created by Jonathan Hopton. Permission must be obtained for their use in any commercial work.

3. THE IMPORTANCE OF REACTION RATE
Being able to speed up or slow down chemical
reactions is important in industry and in everyday life.
Reactions… which take place slowly may need to be speeded up
which are too fast may need to be controlled
may need to be carried out at a lower temperature
to save energy or be safer

4. THE IMPORTANCE OF REACTION RATE
Being able to speed up or slow down chemical
reactions is important in industry and in everyday life.
Reactions… which take place slowly may need to be speeded up
which are too fast may need to be controlled
may need to be carried out at a lower temperature
to save energy or be safer
Changes in temperature concentration of solution
gas pressure surface area of solids
plus the presence of catalysts
all affect the rate of reactions.

5. Explains why the rate of reaction changes
COLLISION THEORY
Explains why the rate of reaction changes
It states ‘particles must COLLIDE before a reaction can take place’
NO COLLISION
No chance of a reaction
taking place
COLLISION
A reaction might
now take place

6. Explains why the rate of reaction changes
COLLISION THEORY
Explains why the rate of reaction changes
It states ‘particles must COLLIDE before a reaction can take place’
‘not all collisions lead to a reaction’
BUT
NO COLLISION
No chance of a reaction
taking place
COLLISION
A reaction might
now take place

7. Explains why the rate of reaction changes
COLLISION THEORY
Explains why the rate of reaction changes
It states ‘particles must COLLIDE before a reaction can take place’
‘not all collisions lead to a reaction’
‘reactants must have at least a minimum amount of energy
known as the ACTIVATION ENERGY in order to react’
BECAUSE

8. Explains why the rate of reaction changes
COLLISION THEORY
Explains why the rate of reaction changes
It states ‘particles must COLLIDE before a reaction can take place’
‘not all collisions lead to a reaction’
‘reactants must have at least a minimum amount of energy
known as the ACTIVATION ENERGY in order to react’
NOT ENOUGH ENERGY
No chance of a reaction
taking place
ENOUGH ENERGY
A reaction will
now take place

9. Explains why the rate of reaction changes
COLLISION THEORY
Explains why the rate of reaction changes
According to collision theory, to increase the rate of reaction you therefore need...

10. Explains why the rate of reaction changes
COLLISION THEORY
Explains why the rate of reaction changes
According to collision theory, to increase the rate of reaction you therefore need...
more frequent collisions

11. Explains why the rate of reaction changes
COLLISION THEORY
Explains why the rate of reaction changes
According to collision theory, to increase the rate of reaction you therefore need...
more frequent collisions increase particle speed
or have more particles present

12. Explains why the rate of reaction changes
COLLISION THEORY
Explains why the rate of reaction changes
According to collision theory, to increase the rate of reaction you therefore need...
more frequent collisions increase particle speed
or have more particles present
more successful collisions

13. Explains why the rate of reaction changes
COLLISION THEORY
Explains why the rate of reaction changes
According to collision theory, to increase the rate of reaction you therefore need...
more frequent collisions increase particle speed
or have more particles present
more successful collisions give particles more energy
or lower the activation energy

14. INCREASING THE RATE OF REACTION The following methods can be used
INCREASE THE SURFACE AREA OF SOLIDS
INCREASE TEMPERATURE
ADD A CATALYST
INCREASE THE CONCENTRATION OF REACTANTS
INCREASE THE PRESSURE OF ANY GASES
SHINE LIGHT (a limited number of reactions)

15. INCREASING SURFACE AREA

16. INCREASING SURFACE AREA
Increasing surface area increases chances of a collision
- more particles are exposed

17. INCREASING SURFACE AREA
Increasing surface area increases chances of a collision
- more particles are exposed
Powdered solids react quicker than larger lumps

18. INCREASING SURFACE AREA
Increasing surface area increases chances of a collision
- more particles are exposed
Powdered solids react quicker than larger lumps
Catalysts (e.g. in catalytic converters) are in a finely
divided form for this reason

19. INCREASING SURFACE AREA
Increasing surface area increases chances of a collision
- more particles are exposed
Powdered solids react quicker than larger lumps
Catalysts (e.g. in catalytic converters) are in a finely
divided form for this reason 1 3 3
SURFACE AREA
= 30 sq units

20. INCREASING SURFACE AREA
Increasing surface area increases chances of a collision
- more particles are exposed
Powdered solids react quicker than larger lumps
Catalysts (e.g. in catalytic converters) are in a finely
divided form for this reason 1 3 3
SURFACE AREA
= 30 sq units

21. INCREASING SURFACE AREA CUT THE SHAPE INTO SMALLER PIECES
Increasing surface area increases chances of a collision
- more particles are exposed
Powdered solids react quicker than larger lumps
Catalysts (e.g. in catalytic converters) are in a finely
divided form for this reason
CUT THE SHAPE INTO SMALLER PIECES 1 3 3
SURFACE AREA
= 30 sq units

22. INCREASING SURFACE AREA CUT THE SHAPE INTO SMALLER PIECES
Increasing surface area increases chances of a collision
- more particles are exposed
Powdered solids react quicker than larger lumps
Catalysts (e.g. in catalytic converters) are in a finely
divided form for this reason 1
CUT THE SHAPE INTO SMALLER PIECES 1 1 1 3 3
SURFACE AREA
= 30 sq units
NEW SURFACE AREA
9 x ( ) = 54 sq units

23. INCREASING SURFACE AREA CUT THE SHAPE INTO SMALLER PIECES
Increasing surface area increases chances of a collision
- more particles are exposed
Powdered solids react quicker than larger lumps
Catalysts (e.g. in catalytic converters) are in a finely
divided form for this reason 1
CUT THE SHAPE INTO SMALLER PIECES 1 1 1 3 3
SURFACE AREA
= 30 sq units
NEW SURFACE AREA
9 x ( ) = 54 sq units

24. INCREASING THE TEMPERATURE

25. INCREASING THE TEMPERATURE
increasing the temperature increases the rate of a reaction
particles get more energy - more overcome the energy barrier
particle speeds also increase - collisions are more frequent

26. INCREASING THE TEMPERATURE ENERGY CHANGES DURING A REACTION
increasing the temperature increases the rate of a reaction
particles get more energy - more overcome the energy barrier
particle speeds also increase - collisions are more frequent
ENERGY CHANGES DURING A REACTION
During a reaction the enthalpy (a form of energy) rises to a maximum, then falls
START OF REATION
END OF REATION

27. INCREASING THE TEMPERATURE
increasing the temperature increases the rate of a reaction
particles get more energy - more overcome the energy barrier
particle speeds also increase - collisions are more frequent
ENERGY CHANGES DURING A REACTION
During a reaction the enthalpy (a form of energy) rises to a maximum, then falls
A minimum of energy is needed to overcome the ACTIVATION ENERGY (Ea)
ACTIVATION ENERGY

28. INCREASING THE TEMPERATURE
increasing the temperature increases the rate of a reaction
particles get more energy - more overcome the energy barrier
particle speeds also increase - collisions are more frequent
ENERGY CHANGES DURING A REACTION
During a reaction the enthalpy (a form of energy) rises to a maximum, then falls
A minimum of energy is needed to overcome the ACTIVATION ENERGY (Ea)
Only reactants with energy equal to, or greater than, this value will react.
ACTIVATION ENERGY

29. INCREASING THE TEMPERATURE
increasing the temperature increases the rate of a reaction
particles get more energy - more overcome the energy barrier
particle speeds also increase - collisions are more frequent
ENERGY CHANGES DURING A REACTION
During a reaction the enthalpy (a form of energy) rises to a maximum, then falls
A minimum of energy is needed to overcome the ACTIVATION ENERGY (Ea)
Only reactants with energy equal to, or greater than, this value will react.
If they don’t have enough energy they will not get over the barrier.
ACTIVATION ENERGY

30. INCREASING THE TEMPERATURE
increasing the temperature increases the rate of a reaction
particles get more energy - more overcome the energy barrier
particle speeds also increase - collisions are more frequent
ENERGY CHANGES DURING A REACTION
During a reaction the enthalpy (a form of energy) rises to a maximum, then falls
A minimum of energy is needed to overcome the ACTIVATION ENERGY (Ea)
Only reactants with energy equal to, or greater than, this value will react.
If they have enough energy they will get over the barrier.
ACTIVATION ENERGY

31. INCREASING THE TEMPERATURE
increasing the temperature increases the rate of a reaction
particles get more energy - more overcome the energy barrier
particle speeds also increase - collisions are more frequent
ENERGY CHANGES DURING A REACTION
During a reaction the enthalpy (a form of energy) rises to a maximum, then falls
A minimum of energy is needed to overcome the ACTIVATION ENERGY (Ea)
Only reactants with energy equal to, or greater than, this value will react.
If more energy is given to the reactants then they are more likely to react.
ACTIVATION ENERGY

32. INCREASING THE TEMPERATURE
increasing the temperature increases the rate of a reaction
particles get more energy - more overcome the energy barrier
particle speeds also increase - collisions are more frequent
ENERGY CHANGES DURING A REACTION
During a reaction the enthalpy (a form of energy) rises to a maximum, then falls
A minimum of energy is needed to overcome the ACTIVATION ENERGY (Ea)
Only reactants with energy equal to, or greater than, this value will react.
If more energy is given to the reactants then they are more likely to react.
ACTIVATION ENERGY

33. ADDING A CATALYST

34. ADDING A CATALYST
Catalysts provide an alternative reaction pathway with a lower
Activation Energy (Ea)

35. ADDING A CATALYST
Catalysts provide an alternative reaction pathway with a lower
Activation Energy (Ea)
Decreasing the Activation Energy means that more particles will
have sufficient energy to overcome the energy barrier and react

36. ADDING A CATALYST
Catalysts provide an alternative reaction pathway with a lower
Activation Energy (Ea)
Decreasing the Activation Energy means that more particles will
have sufficient energy to overcome the energy barrier and react
WITHOUT A CATALYST

37. ADDING A CATALYST
Catalysts provide an alternative reaction pathway with a lower
Activation Energy (Ea)
Decreasing the Activation Energy means that more particles will
have sufficient energy to overcome the energy barrier and react
NEW PATHWAY
WITHOUT A CATALYST
WITH A CATALYST

38. ADDING A CATALYST
Catalysts provide an alternative reaction pathway with a lower
Activation Energy (Ea)
Decreasing the Activation Energy means that more particles will
have sufficient energy to overcome the energy barrier and react
Catalysts remain chemically unchanged at the end of the reaction
- they are not used up

39. ADDING A CATALYST
Catalysts provide an alternative reaction pathway with a lower
Activation Energy (Ea)
Decreasing the Activation Energy means that more particles will
have sufficient energy to overcome the energy barrier and react
Catalysts remain chemically unchanged at the end of the reaction
- they are not used up
Using catalysts avoids the need for extra heat - safer and cheaper

40. ADDING A CATALYST
Catalysts provide an alternative reaction pathway with a lower
Activation Energy (Ea)
Decreasing the Activation Energy means that more particles will
have sufficient energy to overcome the energy barrier and react
Catalysts remain chemically unchanged at the end of the reaction
- they are not used up
Using catalysts avoids the need for extra heat - safer and cheaper
They are used in industry especially where an increase in
temperature results in a lower yield due to a shift in equilibrium

41. ADDING A CATALYST
Catalysts provide an alternative reaction pathway with a lower
Activation Energy (Ea)
Decreasing the Activation Energy means that more particles will
have sufficient energy to overcome the energy barrier and react
Catalysts remain chemically unchanged at the end of the reaction
- they are not used up
Using catalysts avoids the need for extra heat - safer and cheaper
They are used in industry especially where an increase in
temperature results in a lower yield due to a shift in equilibrium
Examples include the Haber and Contact Processes

42. CATALYSTS – USEFUL POINTS
Catalysts are widely used in industry because they…
1 Allow reactions to take place SAVE ENERGY (lower Ea)
at lower temperatures REDUCE CO2 OUTPUT
2 Enable different reactions to be used BETTER ATOM ECONOMY
REDUCE WASTE
3 Are often enzymes GENERATE SPECIFIC PRODUCTS
OPERATE EFFECTIVELY AT ROOM TEMPS
4 Have great economic importance POLY(ETHENE)
in the industrial production of SULPHURIC ACID
AMMONIA
ETHANOL
5 Can reduce pollution CATALYTIC CONVERTERS

43. INCREASING THE CONCENTRATION OF SOLUTIONS

44. INCREASING THE CONCENTRATION OF SOLUTIONS
Increasing concentration = more frequent collisions
= increased rate of reaction
Low concentration
fewer collisions
Higher concentration
more collisions
= FASTER

45. INCREASING THE PRESSURE OF GASES

46. INCREASING THE PRESSURE OF GASES
increasing the pressure forces gas particles closer together

47. INCREASING THE PRESSURE OF GASES
increasing the pressure forces gas particles closer together
this increases the frequency of collisions so the rate increases

48. INCREASING THE PRESSURE OF GASES
increasing the pressure forces gas particles closer together
this increases the frequency of collisions so the rate increases
many industrial processes occur at high pressure to increase
the rate... but it can adversely affect the yield

49. INCREASING THE PRESSURE OF GASES
increasing the pressure forces gas particles closer together
this increases the frequency of collisions so the rate increases
many industrial processes occur at high pressure to increase
the rate... but it can adversely affect the yield

50. INCREASING THE PRESSURE OF GASES
increasing the pressure forces gas particles closer together
this increases the frequency of collisions so the rate increases
many industrial processes occur at high pressure to increase
the rate... but it can adversely affect the yield
more particles in a given volume = greater pressure

51. INCREASING THE PRESSURE OF GASES
increasing the pressure forces gas particles closer together
this increases the frequency of collisions so the rate increases
many industrial processes occur at high pressure to increase
the rate... but it can adversely affect the yield
more particles in a given volume = greater pressure
greater pressure = more frequent collisions

52. INCREASING THE PRESSURE OF GASES
increasing the pressure forces gas particles closer together
this increases the frequency of collisions so the rate increases
many industrial processes occur at high pressure to increase
the rate... but it can adversely affect the yield
more particles in a given volume = greater the pressure
greater pressure = more frequent collisions
more frequent collisions = greater chance of a reaction

53. THE EFFECT OF LIGHT ON CHEMICAL REACTIONS

54. THE EFFECT OF LIGHT ON CHEMICAL REACTIONS
Shining a suitable light source can speed up some reactions
The light provides energy to break bonds and start a reaction
The greater the intensity of the light, the greater the effect
Examples PHOTOSYNTHESIS
DARKENING OF SILVER SALTS IN B/W PHOTOGRAPHY

55. MEASURING REACTION RATES

56. MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration of the reactants drops.

57. MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration of the reactants drops.
Consider the reaction A B C

58. MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration of the reactants drops.
Consider the reaction A B C
Reactants (A and B) Product (C)

59. MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration of the reactants drops.
Consider the reaction A B C
Reactants (A and B) Product (C)
Concentration decreases Concentration increases
TIME
CONCENTRATION B A C

60. MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration of the reactants drops.
Consider the reaction A B C
Reactants (A and B) Product (C)
Concentration decreases Concentration increases
steeper curve = faster reaction
TIME
CONCENTRATION B A C

61. MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration of the reactants drops.
Consider the reaction A B C
Reactants (A and B) Product (C)
Concentration decreases Concentration increases
steeper curve = faster reaction
reactions start off quickly
because of the greater chance
of a collision
TIME
CONCENTRATION B A C

62. MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration of the reactants drops.
Consider the reaction A B C
Reactants (A and B) Product (C)
Concentration decreases Concentration increases
steeper curve = faster reaction
reactions start off quickly
because of the greater chance
of a collision
reactions slow down as there
are fewer reactants to collide
TIME
CONCENTRATION B A C

63. MEASURING REACTION RATES
The rate of a chemical reaction can be found by measuring the amount of a reactant used or the amount of product formed over time.
eg rate of reaction = amount of reactant used
time
or = amount of product formed

64. MEASURING REACTION RATES
RATE How much concentration changes with time.
THE SLOPE OF THE GRADIENT OF THE CURVE GETS LESS AS THE REACTION SLOWS DOWN WITH TIME
CONCENTRATION y x
gradient (slope) = y x
TIME
the rate is found from the slope (gradient) of the curve
the slope at the start of the reaction will give the INITIAL RATE
the slope gets less as the reaction proceeds

65. INTERPRETING GRAPHS INVOLVING RATES

66. INTERPRETING GRAPHS INVOLVING RATES
Magnesium turnings are added to dilute dilute hydrochloric acid and the volume of hydrogen gas produced is measured at set times

67. INTERPRETING GRAPHS INVOLVING RATESC B A
At the start of the reaction the concentrations are at a maximum so the graph will have the STEEPEST SLOPE A

68. INTERPRETING GRAPHS INVOLVING RATESC B B
As the reactants are used up the collisions go down and the rate drops steadily – CURVE STEADILY GETS LESS STEEP A

69. INTERPRETING GRAPHS INVOLVING RATESC B C
At the end of the reaction, all the reactants have been used – no more gas is produced and the CURVE IS LEVEL A

70. QUESTIONS ABOUT RATE GRAPHS
Reaction between magnesium and hydrochloric acid
IN THE FOLLOWING GRAPHS YOU WILL BE TOLD THE CONDITIONS THAT PRODUCE GRAPH X AND BE GIVEN A SET OF OTHER CONDITIONS.
YOU WILL HAVE TO MATCH THE CONDITIONS TO THE GRAPHS A, B and C

71. QUESTIONS ABOUT RATE GRAPHS CONCENTRATION EFFECTS
X 2g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 25°C
2g of magnesium turnings + 50cm3 2M hydrochloric acid (excess) at 25°C
1g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 25°C

72. QUESTIONS ABOUT RATE GRAPHS CONCENTRATION EFFECTS
X 2g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 25°C
2g of magnesium turnings + 50cm3 2M hydrochloric acid (excess) at 25°C
1g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 25°C

73. QUESTIONS ABOUT RATE GRAPHS
TEMPERATURE EFFECTS
X 2g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 35°C
2g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 25°C
2g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 55°C

74. QUESTIONS ABOUT RATE GRAPHS
TEMPERATURE EFFECTS
X 2g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 35°C
2g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 25°C
2g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 55°C

75. QUESTIONS ABOUT RATE GRAPHS
PARTICLE SIZE EFFECTS
X 2g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 25°C
2g of magnesium ribbon + 50cm3 1M hydrochloric acid (excess) at 25°C
2g of magnesium powder + 50cm3 1M hydrochloric acid (excess) at 25°C
2.5g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 25°C

76. QUESTIONS ABOUT RATE GRAPHS
PARTICLE SIZE EFFECTS
X 2g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 25°C
2g of magnesium ribbon + 50cm3 1M hydrochloric acid (excess) at 25°C
2g of magnesium powder + 50cm3 1M hydrochloric acid (excess) at 25°C
2.5g of magnesium turnings + 50cm3 1M hydrochloric acid (excess) at 25°C

77. © 2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHING
RATE OF REACTION
THE END
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