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

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Presentation on theme: "RATES OF REACTION A guide for GCSE students 2010 SPECIFICATIONS KNOCKHARDY PUBLISHING."— Presentation transcript:

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

2 RATES 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... 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 temperatureconcentration of solution gas pressuresurface 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’ NO COLLISION No chance of a reaction taking place COLLISION A reaction might now take place BUT

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’ NOT ENOUGH ENERGY No chance of a reaction taking place ENOUGH ENERGY A reaction will now take place

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) 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 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 3 3 SURFACE AREA = 30 sq units 1

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 3 3 SURFACE AREA = 30 sq units 1

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 3 3 SURFACE AREA = 30 sq units 1

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 CUT THE SHAPE INTO SMALLER PIECES 3 3 SURFACE AREA = 30 sq units NEW SURFACE AREA 9 x ( ) = 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 CUT THE SHAPE INTO SMALLER PIECES 3 3 SURFACE AREA = 30 sq units NEW SURFACE AREA 9 x ( ) = 54 sq units

24 INCREASING THE TEMPERATURE

25 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 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

27 INCREASING 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 (E a ) 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

28 INCREASING 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 (E a ) 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

29 INCREASING 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 (E a ) 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

30 INCREASING 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 (E a ) 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

31 INCREASING 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 (E a ) 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

32 INCREASING 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 (E a ) 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

33 ADDING A CATALYST

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

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

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

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

38 Catalysts provide an alternative reaction pathway with a lower Activation Energy (E a ) 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

39 Catalysts provide an alternative reaction pathway with a lower Activation Energy (E a ) 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

40 Catalysts provide an alternative reaction pathway with a lower Activation Energy (E a ) 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

41 Catalysts provide an alternative reaction pathway with a lower Activation Energy (E a ) 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 CATALYST

42 Catalysts are widely used in industry because they… 1 Allow reactions to take place SAVE ENERGY (lower E a ) at lower temperatures REDUCE CO 2 OUTPUT 2 Enable different reactions to be usedBETTER ATOM ECONOMY REDUCE WASTE 3 Are often enzymesGENERATE SPECIFIC PRODUCTS OPERATE EFFECTIVELY AT ROOM TEMPS 4 Have great economic importance POLY(ETHENE) in the industrial production ofSULPHURIC ACID AMMONIA ETHANOL 5 Can reduce pollutionCATALYTIC CONVERTERS CATALYSTS – USEFUL POINTS

43 INCREASING THE CONCENTRATION OF SOLUTIONS

44 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 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 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 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. egrate of reaction = amount of reactant used time or = amount of product formed time

64 RATE How much concentration changes with time. y CONCENTRATION gradient (slope) =y x 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 THE SLOPE OF THE GRADIENT OF THE CURVE GETS LESS AS THE REACTION SLOWS DOWN WITH TIME MEASURING REACTION RATES

65 INTERPRETING GRAPHS INVOLVING RATES

66 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

67 A B C A At the start of the reaction the concentrations are at a maximum so the graph will have the STEEPEST SLOPE A At the start of the reaction the concentrations are at a maximum so the graph will have the STEEPEST SLOPE

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

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

70 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

71 X2g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 25°C 2g of magnesium turnings + 50cm 3 2M hydrochloric acid (excess) at 25°C 1g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 25°C CONCENTRATION EFFECTS QUESTIONS ABOUT RATE GRAPHS

72 CONCENTRATION EFFECTS X2g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 25°C 2g of magnesium turnings + 50cm 3 2M hydrochloric acid (excess) at 25°C 1g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 25°C QUESTIONS ABOUT RATE GRAPHS

73 TEMPERATURE EFFECTS X2g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 35°C 2g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 25°C 2g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 55°C QUESTIONS ABOUT RATE GRAPHS

74 TEMPERATURE EFFECTS X2g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 35°C 2g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 25°C 2g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 55°C QUESTIONS ABOUT RATE GRAPHS

75 PARTICLE SIZE EFFECTS X2g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 25°C 2g of magnesium ribbon + 50cm 3 1M hydrochloric acid (excess) at 25°C 2g of magnesium powder + 50cm 3 1M hydrochloric acid (excess) at 25°C 2.5g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 25°C QUESTIONS ABOUT RATE GRAPHS

76 PARTICLE SIZE EFFECTS X2g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 25°C 2g of magnesium ribbon + 50cm 3 1M hydrochloric acid (excess) at 25°C 2g of magnesium powder + 50cm 3 1M hydrochloric acid (excess) at 25°C 2.5g of magnesium turnings + 50cm 3 1M hydrochloric acid (excess) at 25°C QUESTIONS ABOUT RATE GRAPHS

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


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