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Boardworks GCSE Additional Science: Chemistry Rates of Reaction

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Presentation on theme: "Boardworks GCSE Additional Science: Chemistry Rates of Reaction"— Presentation transcript:

1 Boardworks GCSE Additional Science: Chemistry Rates of Reaction
8. Kinetics

2 8.1a Collision Theory Learning Objectives
Understand that reactions can only occur when collisions take place between particles having sufficient energy Define the term “activation energy” Understand that most reactions do not lead to a reaction

3 Boardworks GCSE Additional Science: Chemistry Rates of Reaction

4 What does rate of reaction mean?
Boardworks GCSE Additional Science: Chemistry Rates of Reaction The speed of different chemical reactions varies hugely. Some reactions are very fast and others are very slow. The speed of a reaction is called the rate of the reaction. What is the rate of these reactions? rusting baking explosion Photo credit: © 2007 Jupiterimages Corporation slow fast very fast

5 Boardworks GCSE Additional Science: Chemistry Rates of Reaction
Why are some reactions faster than others? Teacher notes This illustration contains several discussion points relating to rates of reaction, including: Red characters: these represent particles that have a large amount of kinetic energy and are therefore likely to react. Blue characters : these represent particles that have a small amount of kinetic energy and are therefore unlikely to react (hence why some are asleep). Bumper cars: the collision between two bumper cars represents the large amount of energy released during a reaction.

6 Reactions, particles and collisions
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Reactions take place when particles collide with a certain amount of energy. The minimum amount of energy needed for the particles to react is called the activation energy, and is different for each reaction. The rate of a reaction depends on two things: the frequency of collisions between particles the energy with which particles collide. Teacher notes See the ‘Energy Transfer’ presentation for more information on activation energy. If particles collide with less energy than the activation energy, they will not react. The particles will just bounce off each other.

7 Not all collisions result in a reaction
Particles may not collide with enough energy (activation energy) Particles may not collide with the correct orientation.

8 Collision Theory

9 Not all collisions result in a reaction

10 The rate of reaction depends on what two factors?
Review The rate of reaction depends on what two factors? Describe collision theory. Describe the term “activation energy”. Why is it that most collisions do not result in a reaction?

11 What is a chemical reaction?
Boardworks GCSE Additional Science: Chemistry Chemical Reactions A chemical reaction is a change that takes place when one or more substances (called reactants) form one or more new substances (called products). reactants products For example: carbon carbon dioxide oxygen +

12 All molecules store chemical energy in the chemical bonds.
Molecules held together by bonds  takes energy to break carbon carbon dioxide oxygen +

13 What is a chemical reaction?
Boardworks GCSE Additional Science: Chemistry Chemical Reactions What is a chemical reaction? Usually two parts to a chemical reaction: Breaking of chemical bonds. Formation of new bonds. + carbon + oxygen carbon dioxide

14 Boardworks GCSE Additional Science: Chemistry Chemical Reactions
Energy Usually two parts to a chemical reaction: Breaking of chemical bonds  Takes Energy Formation of new bonds  Give Out Energy + carbon + oxygen carbon dioxide

15 Endothermic vs. Exothermic
Endothermic = requires energy, process absorbs energy Exothermic = gives out energy, process releases energy (think exo like exit)

16 Making and breaking chemical bonds
Boardworks GCSE Additional Science: Chemistry Energy Transfer Most chemicals will break up (decompose) if they are heated strongly enough. This means that energy is needed to break chemical bonds – an endothermic process. energy absorbed Because bond-breaking is endothermic, bond-making must therefore be exothermic. This means that energy is released when chemical bonds are made. energy released

17 Activation energy = energy needed to start the reaction (break bonds)
High activation energy = need to put in a LOT of energy (strong bonds) Low activation energy = little energy needed, weak bonds

18 Enthalpy Profile Diagram

19 What are the two steps in a chemical reaction?
Review What are the two steps in a chemical reaction? Which absorbs energy? Which releases energy? What do the terms “Exothermic” and “Endothermic” mean?

20 Energy absorbed (activation) > Energy released
Overall Reaction Endothermic Reactions Energy absorbed (activation) > Energy released  Overall energy absorbed (feels cold) Exothermic Reactions Energy absorbed (activation) < Energy released  Overall energy released (feels hot)

21 Exothermic reactions An exothermic reaction is one which releases heat energy to the surroundings The temperature of the surroundings increases The energy released from forming new bonds is greater than the energy needed to break old bonds Exothermic reactions

22 Exothermic reactions Exothermic reactions

23 Boardworks GCSE Additional Science: Chemistry Energy Transfer
Exothermic reactions Exothermic reactions release thermal energy (heat) into their surroundings. Exothermic reactions can occur spontaneously and some are explosive. What are some examples? combustion respiration neutralization of acids with alkalis reactions of metals with acids the Thermit Process. Photo credit: Jupiterimages Corporation Teacher notes The Thermit Process is a displacement reaction between aluminium and iron oxide, and is used in welding iron and steel. See the ‘Chemical Reactions’ presentation for more information on the Thermit Process. See the GCSE Science (Chemistry) ‘Combustion and Alternative Fuels’ presentation for more information on combustion.

24 Endothermic reactions
An endothermic reaction is on which takes in heat energy from the surroundings The temperature of the surroundings decreases The energy needed to break old bonds is greater than the energy released from forming new bonds Endothermic reactions

25 Endothermic reactions

26 Endothermic reactions
Boardworks GCSE Additional Science: Chemistry Energy Transfer Endothermic reactions absorb thermal energy, and so cause a decrease in temperature. What are some examples? thermal decomposition, e.g. calcium carbonate in a blast furnace photosynthesis some types of electrolysis sherbet! Photo credit: Janet Goulden Teacher notes Endothermic reactions must absorb energy in order to proceed, and so cannot occur spontaneously. Melting, boiling, and evaporation are examples of endothermic changes of state, but not chemical reactions. Sherbet is made from sugar, bicarbonate of soda and powdered citric acid. When the acid and bicarbonate of soda dissolve in saliva, they produce fizzing sodium citrate, water and carbon dioxide, and a cooling sensation on the tongue.

27

28 Exothermic reactions Exothermic reactions

29 Endothermic reactions

30 8.1b Rates of Reaction Learning Objectives
Understand the effect of temperature on rate of reaction. Understand the effect of concentration on rate of reaction.

31 Changing the rate of reactions
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Anything that increases the number of successful collisions between reactant particles will speed up a reaction. What factors affect the rate of reactions? increased temperature increased concentration of dissolved reactants, and increased pressure of gaseous reactants increased surface area of solid reactants use of a catalyst.

32 Boardworks GCSE Additional Science: Chemistry Rates of Reaction

33 Temperature and collisions
Boardworks GCSE Additional Science: Chemistry Rates of Reaction How does temperature affect the rate of particle collision?

34 Effect of temperature on rate
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Higher temperature = higher rate of reaction Why does increased temperature increase the rate of reaction? higher temperature = more energy more energy = faster particles faster particles = more frequent collisions  more successful collisions = more reactions. Also... more total energy = more collision with enough Ea (more forceful collisions.

35 Temperature and particle collisions
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This simulation illustrates how increasing the temperature increases the number of collisions between particles.

36 Temperature and batteries
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Why are batteries more likely to rundown more quickly in cold weather? At low temperatures the reaction that generates the electric current proceeds more slowly than at higher temperatures. Photo credit: © 2007 Jupiterimages Corporation If a battery is not in use it will discharge more slowly at low temperatures than at higher temperatures. However, if a battery needs to be used at low temperatures then warming it up speeds up the reaction that generates the electric current, giving you more power. This means batteries are less likely to deliver enough current to meet demand.

37 How does temperature affect rate?
Boardworks GCSE Additional Science: Chemistry Rates of Reaction The reaction between sodium thiosulfate and hydrochloric acid produces sulfur. hydrochloric acid sodium chloride sulfur sodium thiosulfate + water sulfur dioxide Na2S2O3 (aq) 2HCl (aq) 2NaCl (aq) S (s) + SO2 (g) H2O (l) Sulfur is solid and so it turns the solution cloudy. How can this fact be used to measure the effect of temperature on rate of reaction?

38 The effect of temperature on rate
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This animation can be used to introduce the reaction between sodium thiosulfate and hydrochloric acid as a way of measuring the effect of temperature on rate of reaction. It could be shown as precursor to running the experiment in the lab, or as a revision exercise.

39 Boardworks GCSE Additional Science: Chemistry Rates of Reaction

40 Effect of concentration on rate of reaction
Boardworks GCSE Additional Science: Chemistry Rates of Reaction higher the concentration = faster rate of a reaction Why does increased concentration increase the rate of reaction? higher concentration = more particles more likely to collide  more likely to react. lower concentration higher concentration

41 Concentration and particle collisions
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This simulation illustrates how increasing the concentration increases the number of collisions between particles.

42 The effect of concentration on rate
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This animation can be used to introduce the reaction between magnesium and hydrochloric acid as a way of measuring the effect of concentration on rate of reaction. It could be shown as precursor to running the experiment in the lab, or as a revision exercise.

43 Effect of pressure on rate of reaction
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Why does increasing the pressure of gaseous reactants increase the rate of reaction? As the pressure increases, the space in which the gas particles are moving becomes smaller. The gas particles become closer together, increasing the frequency of collisions. This means that the particles are more likely to react. lower pressure higher pressure

44 Boardworks GCSE Additional Science: Chemistry Rates of Reaction

45 Effect of surface area on rate of reaction
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Any reaction involving a solid can only take place at the surface of the solid. If the solid is split into several pieces, the surface area increases. What effect will this have on rate of reaction? low surface area high surface area larger SA = larger area for the reactant particles to collide with = faster rate of reaction smaller the pieces = larger the surface area = more collisions  greater chance of reaction.

46 Surface area and particle collisions
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This simulation illustrates how increasing the surface area increases the number of collisions between particles and solid reactants

47 Reaction between a carbonate and acid
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Marble chips are made of calcium carbonate. They react with hydrochloric acid to produce carbon dioxide. hydrochloric acid calcium chloride calcium carbonate + water carbon dioxide CaCO3 (aq) 2HCl (aq) CaCl2 (aq) + H2O (aq) CO2 (g) The effect of increasing surface area on the rate of reaction can be measured by comparing how quickly the mass of the reactants decreases using marble chips of different sizes.

48 The effect of surface area on rate
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This animation can be used to introduce the reaction between marble chips (calcium carbonate) and hydrochloric acid as a way of measuring the effect of surface on rate of reaction. It could be shown as precursor to running the experiment in the lab, or as a revision exercise.

49 8.2 Maxwell-Boltzman distribution
Learning Objectives Have a qualitative understanding of the Maxwell-Boltzman distribution of molecular energies in gases. Be able to draw and interpret distribution curves for different temperatures.

50 Maxwell-Boltzman distribution curve

51 Effect of temperature

52 8.3 Catalysts Learning Objectives
Know the meaning of the term catalyst. Understand how catalysts work to increase the rate of reaction.

53 Boardworks GCSE Additional Science: Chemistry Rates of Reaction
What are catalysts? Boardworks GCSE Additional Science: Chemistry Rates of Reaction Catalysts are substances that change the rate of a reaction without being used up in the reaction. Catalysts never produce more product – they just produce the same amount more quickly. reaction (time) energy (kJ) Ea without catalyst Different catalysts work in different ways, but most lower the reaction’s activation energy (Ea). Ea with catalyst Teacher notes See the ‘Energy Transfer’ presentation for more information on activation energy.

54 Effect of catalyst

55 How does a catalyst speed of a reaction?
Catalysts provide an alternate reaction pathway. They lower the activation energy required to start the reaction. Catalysts are reformed at the end of the reaction, they are not used up so are not considered reactants.

56 Boardworks GCSE Additional Science: Chemistry Rates of Reaction
Everyday catalysts Boardworks GCSE Additional Science: Chemistry Rates of Reaction Many catalysts are transition metals or their compounds. For example: Nickel is a catalyst in the production of margarine (hydrogenation of vegetable oils). Iron is a catalyst in the production of ammonia from nitrogen and hydrogen (the Haber process). Platinum is a catalyst in the catalytic converters of car exhausts. It catalyzes the conversion of carbon monoxide and nitrogen oxide into the less polluting carbon dioxide and nitrogen. Photo credit: © 2007 Jupiterimages Corporation Teacher notes See the ‘Reversible Reactions’ presentation for more information on the Haber process.

57 Boardworks GCSE Additional Science: Chemistry Rates of Reaction
Catalysts in industry Boardworks GCSE Additional Science: Chemistry Rates of Reaction Why are catalysts so important for industry? Products can be made more quickly, saving time and money. Catalysts reduce the need for high temperatures, saving fuel and reducing pollution. Teacher notes See the ‘Enzymes’ Biology presentation for more information on enzymes as catalysts and their use in industrial processes. Catalysts are also essential for living cells. Biological catalysts are special types of protein called enzymes.

58 Collisions and reactions: summary
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This completing sentences activity could be used as a plenary or revision exercise on rates of reaction. Students could be asked to write down the missing words in their books and the activity could be concluded by the completion on the IWB.

59 Boardworks GCSE Additional Science: Chemistry Rates of Reaction
Glossary Boardworks GCSE Additional Science: Chemistry Rates of Reaction activation energy – The amount of energy needed to start a reaction. catalyst – A substance that increases the rate of a chemical reaction without being used up. concentration – The number of molecules of a substance in a given volume. enzyme – A biological catalyst. rate of reaction – The change in the concentration over a certain period of time.

60 Boardworks GCSE Additional Science: Chemistry Rates of Reaction
Anagrams Boardworks GCSE Additional Science: Chemistry Rates of Reaction

61 Rates of reaction: summary
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This completing sentences activity provides the opportunity for some informal assessment of students’ understanding of rates of reaction.

62 Boardworks GCSE Additional Science: Chemistry Rates of Reaction
Multiple-choice quiz Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This multiple-choice quiz could be used as a plenary activity to assess students’ understanding of rates of reaction. The questions can be skipped through without answering by clicking “next”. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.

63 Kinetics Quiz 1 Define the term activation energy.
2 Draw, with labelled axes the Maxwell-Boatman distribution. Label this T1. Draw on the same axes a curve to represent same sample at lower temperature. 3 Add a label for activation energy. 4 Draw the effect of adding a catalyst. 5 Explain why most collisions do not result in a reaction. 6 Describe three ways to increase the rate of reaction and explain why using ideas about collision theory.


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