RATES OF REACTION

1
RATES OF REACTION
2
RATES OF REACTION
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
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
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
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
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
9
COLLISION THEORY
Explains why the rate of reaction
changes According to collision theory, to
increase the rate of reaction you therefore
need...
10
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
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
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
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 993333 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 993333 30 sq units
21
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

CUT THE SHAPE INTO SMALLER PIECES
1
3
3
SURFACE AREA 993333 30 sq units
22
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
CUT THE SHAPE INTO SMALLER PIECES
1
1
1
3
3
SURFACE AREA 993333 30 sq units
NEW SURFACE AREA 9 x (111111) 54 sq units
23
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
CUT THE SHAPE INTO SMALLER PIECES
1
1
1
3
3
SURFACE AREA 993333 30 sq units
NEW SURFACE AREA 9 x (111111) 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

• 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
dont 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 ET
HANOL 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

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
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

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

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

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
time
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
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 RATES
C
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 RATES
C
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 RATES
C
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 25C 2g of
magnesium turnings 50cm3 2M hydrochloric acid
(excess) at 25C 1g of magnesium turnings
50cm3 1M hydrochloric acid (excess) at 25C
72
QUESTIONS ABOUT RATE GRAPHS
CONCENTRATION EFFECTS
X 2g of magnesium turnings 50cm3 1M
hydrochloric acid (excess) at 25C 2g of
magnesium turnings 50cm3 2M hydrochloric acid
(excess) at 25C 1g of magnesium turnings
50cm3 1M hydrochloric acid (excess) at 25C
73
QUESTIONS ABOUT RATE GRAPHS
TEMPERATURE EFFECTS
X 2g of magnesium turnings 50cm3 1M
hydrochloric acid (excess) at 35C 2g of
magnesium turnings 50cm3 1M hydrochloric acid
(excess) at 25C 2g of magnesium turnings
50cm3 1M hydrochloric acid (excess) at 55C
74
QUESTIONS ABOUT RATE GRAPHS
TEMPERATURE EFFECTS
X 2g of magnesium turnings 50cm3 1M
hydrochloric acid (excess) at 35C 2g of
magnesium turnings 50cm3 1M hydrochloric acid
(excess) at 25C 2g of magnesium turnings
50cm3 1M hydrochloric acid (excess) at 55C
75
QUESTIONS ABOUT RATE GRAPHS
PARTICLE SIZE EFFECTS
X 2g of magnesium turnings 50cm3 1M
hydrochloric acid (excess) at 25C 2g of
magnesium ribbon 50cm3 1M hydrochloric acid
(excess) at 25C 2g of magnesium powder 50cm3
1M hydrochloric acid (excess) at 25C 2.5g of
magnesium turnings 50cm3 1M hydrochloric acid
(excess) at 25C
76
QUESTIONS ABOUT RATE GRAPHS
PARTICLE SIZE EFFECTS
X 2g of magnesium turnings 50cm3 1M
hydrochloric acid (excess) at 25C 2g of
magnesium ribbon 50cm3 1M hydrochloric acid
(excess) at 25C 2g of magnesium powder 50cm3
1M hydrochloric acid (excess) at 25C 2.5g of
magnesium turnings 50cm3 1M hydrochloric acid
(excess) at 25C
77
RATE OF REACTION THE END