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

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... 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.

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 concentration of solution gas pressure surface area of solids plus the presence of catalysts all affect the rate of reactions.

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

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

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

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

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...

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

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

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

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

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 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 9+9+3+3+3+3 = 30 sq units

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 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 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 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 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

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 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

INCREASING THE CONCENTRATION OF SOLUTIONS

INCREASING THE CONCENTRATION OF SOLUTIONS Increasing concentration = more frequent collisions = increased rate of reaction Low concentration fewer collisions 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 A + B C Reactants (A and B) 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 C Reactants (A and B) Product (C) Concentration decreases Concentration increases TIME CONCENTRATION B A 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 C Reactants (A and B) Product (C) Concentration decreases Concentration increases steeper curve = faster reaction TIME CONCENTRATION B A 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 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

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

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

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

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

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