RATES OF RATES OF REACTIONREACTION

A guide for GCSE studentsA guide for GCSE students

2010 2010 SPECIFICATIONSSPECIFICATIONSKNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING

RATES OF REACTIONRATES OF REACTION

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...

www.knockhardy.org.uk

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.

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.

THE IMPORTANCE OF REACTION RATETHE IMPORTANCE OF REACTION RATE

Being able to speed up or slow down chemicalreactions 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 temperatureto save energy or be safer

THE IMPORTANCE OF REACTION RATETHE IMPORTANCE OF REACTION RATE

Being able to speed up or slow down chemicalreactions 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 temperatureto save energy or be safer

Changes in temperature concentration of solutiongas pressure surface area of solids

plus the presence of catalysts

all affect the rate of reactions.

COLLISION THEORYCOLLISION THEORY

Explains why the rate of reaction changes

It states ‘particles must COLLIDE before a reaction can take place’

NO COLLISIONNo chance of a reaction

taking place

COLLISIONA reaction mightnow take place

COLLISION THEORYCOLLISION 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’

NO COLLISIONNo chance of a reaction

taking place

COLLISIONA reaction mightnow take place

BUT

COLLISION THEORYCOLLISION 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

COLLISION THEORYCOLLISION 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 ENERGYNo chance of a reaction

taking place

ENOUGH ENERGYA reaction willnow take place

COLLISION THEORYCOLLISION THEORY

Explains why the rate of reaction changes

According to collision theory, to increase the rate of reaction you therefore need...

COLLISION THEORYCOLLISION 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 THEORYCOLLISION 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

COLLISION THEORYCOLLISION 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

COLLISION THEORYCOLLISION 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

INCREASING THE RATE OF REACTIONINCREASING 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)

• 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 AREAINCREASING SURFACE AREA

INCREASING SURFACE AREAINCREASING SURFACE AREA

• Increasing surface area increases chances of a collision - more particles are exposed

INCREASING SURFACE AREAINCREASING SURFACE AREA

• Increasing surface area increases chances of a collision - more particles are exposed

• Powdered solids react quicker than larger lumps

INCREASING SURFACE AREAINCREASING 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 AREAINCREASING 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

3

3

SURFACE AREA9+9+3+3+3+3 = 30 sq units

1

INCREASING SURFACE AREAINCREASING 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

3

3

SURFACE AREA9+9+3+3+3+3 = 30 sq units

1

INCREASING SURFACE AREAINCREASING 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

3

3

SURFACE AREA9+9+3+3+3+3 = 30 sq units

1

INCREASING SURFACE AREAINCREASING 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

3

3

SURFACE AREA9+9+3+3+3+3 = 30 sq units

NEW SURFACE AREA9 x (1+1+1+1+1+1) = 54 sq units

1

111

INCREASING SURFACE AREAINCREASING 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

3

3

SURFACE AREA9+9+3+3+3+3 = 30 sq units

NEW SURFACE AREA9 x (1+1+1+1+1+1) = 54 sq units

1

111

INCREASING THE TEMPERATUREINCREASING THE TEMPERATURE

INCREASING THE TEMPERATUREINCREASING 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 TEMPERATUREINCREASING THE TEMPERATURE

ENERGY CHANGES DURING A REACTION

During a reaction the enthalpy (a form of energy) rises to a maximum, then falls

• 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

START OF REATION

END OF REATION

INCREASING THE TEMPERATUREINCREASING THE TEMPERATURE

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)

• 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

ACTIVATION ENERGY

INCREASING THE TEMPERATUREINCREASING THE TEMPERATURE

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.

• 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

ACTIVATION ENERGY

INCREASING THE TEMPERATUREINCREASING THE TEMPERATURE

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.

• 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

ACTIVATION ENERGY

INCREASING THE TEMPERATUREINCREASING THE TEMPERATURE

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.

• 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

ACTIVATION ENERGY

INCREASING THE TEMPERATUREINCREASING THE TEMPERATURE

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.

• 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

ACTIVATION ENERGY

INCREASING THE TEMPERATUREINCREASING THE TEMPERATURE

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.

• 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

ACTIVATION ENERGY

ADDING A CATALYSTADDING A CATALYST

• Catalysts provide an alternative reaction pathway with a lower Activation Energy (Ea)

ADDING A CATALYSTADDING 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 CATALYSTADDING 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 CATALYSTADDING A CATALYST

WITHOUT 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 CATALYSTADDING A CATALYST

WITHOUT A CATALYST WITH A CATALYST

NEW PATHWAY

• 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 CATALYSTADDING 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 CATALYSTADDING 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 CATALYSTADDING 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

ADDING A CATALYSTADDING A CATALYST

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 ECONOMYREDUCE WASTE

3 Are often enzymes GENERATE SPECIFIC PRODUCTSOPERATE EFFECTIVELY AT ROOM TEMPS

4 Have great economic importance POLY(ETHENE) in the industrial production of SULPHURIC ACID

AMMONIAETHANOL

5 Can reduce pollution CATALYTIC CONVERTERS

CATALYSTS – CATALYSTS – USEFUL POINTSUSEFUL POINTS

INCREASING THE CONCENTRATION OF SOLUTIONSINCREASING THE CONCENTRATION OF SOLUTIONS

INCREASING THE CONCENTRATION OF SOLUTIONSINCREASING THE CONCENTRATION OF SOLUTIONS

Increasing concentration = more frequent collisions = increased rate of reaction

Low concentrationfewer collisions

Higher concentrationmore collisions

= FASTER

INCREASING THE PRESSURE OF GASESINCREASING THE PRESSURE OF GASES

INCREASING THE PRESSURE OF GASESINCREASING THE PRESSURE OF GASES

• increasing the pressure forces gas particles closer together

INCREASING THE PRESSURE OF GASESINCREASING 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 GASESINCREASING 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 GASESINCREASING 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 GASESINCREASING 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 GASESINCREASING 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 GASESINCREASING 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 REACTIONSTHE EFFECT OF LIGHT ON CHEMICAL REACTIONS

THE EFFECT OF LIGHT ON CHEMICAL REACTIONSTHE 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 RATESMEASURING REACTION RATES

MEASURING REACTION RATESMEASURING REACTION RATES

Reactions are fastest at the start and get slower as the concentration of the reactants drops.

MEASURING REACTION RATESMEASURING 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 RATESMEASURING 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)

MEASURING REACTION RATESMEASURING 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

CO

NC

EN

TR

AT

ION

B A

C

MEASURING REACTION RATESMEASURING 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

CO

NC

EN

TR

AT

ION

B A

C

MEASURING REACTION RATESMEASURING 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

CO

NC

EN

TR

AT

ION

B A

C

MEASURING REACTION RATESMEASURING 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

CO

NC

EN

TR

AT

ION

B A

C

MEASURING REACTION RATESMEASURING 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

INTERPRETING GRAPHS INVOLVING RATESINTERPRETING GRAPHS INVOLVING RATES

Magnesium turnings are added to dilute dilute hydrochloric acid and

the volume of hydrogen gas produced is measured at set times

Magnesium turnings are added to dilute dilute hydrochloric acid and

the volume of hydrogen gas produced is measured at set times

INTERPRETING GRAPHS INVOLVING RATESINTERPRETING GRAPHS INVOLVING RATES

A

B

C

INTERPRETING GRAPHS INVOLVING RATESINTERPRETING GRAPHS INVOLVING RATES

AAt the start of the reaction the

concentrations are at a maximum so the graph will have the STEEPEST SLOPE

AAt the start of the reaction the

concentrations are at a maximum so the graph will have the STEEPEST SLOPE

A

B

C

INTERPRETING GRAPHS INVOLVING RATESINTERPRETING GRAPHS INVOLVING RATES

BAs the reactants are used up

the collisions go down and the rate drops steadily – CURVE

STEADILY GETS LESS STEEP

BAs the reactants are used up

the collisions go down and the rate drops steadily – CURVE

STEADILY GETS LESS STEEP

A

B

C

INTERPRETING GRAPHS INVOLVING RATESINTERPRETING GRAPHS INVOLVING RATES

CAt the end of the reaction, all

the reactants have been used – no more gas is produced and

the CURVE IS LEVEL

CAt the end of the reaction, all

the reactants have been used – no more gas is produced and

the CURVE IS LEVEL

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 GRAPHSQUESTIONS ABOUT RATE GRAPHS

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

CONCENTRATION EFFECTSQUESTIONS ABOUT RATE GRAPHSQUESTIONS 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 GRAPHSQUESTIONS 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 GRAPHSQUESTIONS 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 GRAPHSQUESTIONS 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 GRAPHSQUESTIONS 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 GRAPHSQUESTIONS ABOUT RATE GRAPHS

© 2011 © 2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHINGJONATHAN HOPTON & KNOCKHARDY PUBLISHING

RATE OF RATE OF REACTIONREACTION

THE ENDTHE END