Transcript Collision Theory - SchoolWorld an Edline Solution

RATES OF
REACTION
Collision Theory
Activation Energy
2
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
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
gas pressure
concentration of solution
surface area of solids
plus the presence of catalysts
all affect the rate of reactions.
COLLISION THEORY
Explains why the rate of reaction changes
It states
‘particles must COLLIDE before a reaction can take place’
NO COLLISION
COLLISION
No chance of a reaction
taking place
A reaction might
now take place
COLLISION THEORY
Explains why the rate of reaction changes
It states
‘particles must COLLIDE before a reaction can take place’
BUT ‘not all collisions lead to a reaction’
NO COLLISION
COLLISION
No chance of a reaction
taking place
A reaction might
now take place
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’
BECAUSE ‘reactants must have at least a minimum amount of energy
known as the ACTIVATION ENERGY in order to react’
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
ENOUGH ENERGY
No chance of a reaction
taking place
A reaction will
now take place
COLLISION THEORY
Explains why the rate of reaction changes
According to collision theory, to increase the rate of reaction you
therefore need...
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
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
or
increase particle speed
have more particles present
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
or
more successful collisions
increase particle speed
have more particles present
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
or
increase particle speed
have more particles present
or
give particles more energy
lower the activation energy
more successful collisions
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)
INCREASING SURFACE AREA
INCREASING SURFACE AREA
• Increasing surface area increases chances of a collision
- more particles are exposed
INCREASING SURFACE AREA
• Increasing surface area increases chances of a collision
- more particles are exposed
• Powdered solids react quicker than larger lumps
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
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
9+9+3+3+3+3 = 30 sq units
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
9+9+3+3+3+3 = 30 sq units
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
9+9+3+3+3+3 = 30 sq units
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
1
1
1
3
3
SURFACE AREA
9+9+3+3+3+3 = 30 sq units
NEW SURFACE AREA
9 x (1+1+1+1+1+1) = 54 sq units
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
1
1
1
3
3
SURFACE AREA
9+9+3+3+3+3 = 30 sq units
NEW SURFACE AREA
9 x (1+1+1+1+1+1) = 54 sq units
INCREASING THE TEMPERATURE
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
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
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
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
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
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
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
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
ADDING A CATALYST
ADDING A CATALYST
• Catalysts provide an alternative reaction pathway with a lower
Activation Energy (Ea)
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
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
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
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
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
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
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
CATALYSTS – USEFUL POINTS
Catalysts are widely used in industry because they…
1 Allow reactions to take place
at lower temperatures
SAVE ENERGY (lower Ea)
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
in the industrial production of
POLY(ETHENE)
SULPHURIC ACID
AMMONIA
ETHANOL
5 Can reduce pollution
CATALYTIC CONVERTERS
INCREASING THE CONCENTRATION OF SOLUTIONS
INCREASING THE CONCENTRATION OF SOLUTIONS
Increasing concentration
Low concentration
fewer collisions
= more frequent collisions
= increased rate of reaction
Higher concentration
more collisions
= FASTER
INCREASING THE PRESSURE OF GASES
INCREASING THE PRESSURE OF GASES
• increasing the pressure forces gas particles closer together
INCREASING THE PRESSURE OF GASES
• increasing the pressure forces gas particles closer together
• this increases the frequency of collisions so the rate increases
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
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
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
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
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
THE EFFECT OF LIGHT ON CHEMICAL REACTIONS
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
MEASURING REACTION RATES
MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration
of the reactants drops.
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
MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration
of the reactants drops.
Consider the reaction
Reactants (A and B)
A
+
B
C
Product (C)
MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration
of the reactants drops.
Consider the reaction
A
+
B
Product (C)
Concentration increases
CONCENTRATION
Reactants (A and B)
Concentration decreases
C
C
A
B
TIME
MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration
of the reactants drops.
Consider the reaction
A
+
B
Reactants (A and B)
Concentration decreases
C
Product (C)
Concentration increases
CONCENTRATION
• steeper curve = faster reaction
C
A
B
TIME
MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration
of the reactants drops.
Consider the reaction
A
+
B
Reactants (A and B)
Concentration decreases
C
Product (C)
Concentration increases
• reactions start off quickly
because of the greater chance
of a collision
CONCENTRATION
• steeper curve = faster reaction
C
A
B
TIME
MEASURING REACTION RATES
Reactions are fastest at the start and get slower as the concentration
of the reactants drops.
Consider the reaction
A
+
B
Reactants (A and B)
Concentration decreases
C
Product (C)
Concentration increases
• reactions start off quickly
because of the greater chance
of a collision
• reactions slow down as there
are fewer reactants to collide
CONCENTRATION
• steeper curve = faster reaction
C
A
B
TIME
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
or
=
amount of reactant used
time
=
amount of product formed
time
INTERPRETING GRAPHS INVOLVING RATES
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
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
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
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
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
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
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
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
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
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
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
RATE OF
REACTION
THE END
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