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1. Slide 1: Science Interactive LTD Copyright 2005 Science Interactive LTD Science base multimedia CD-ROM for PC is a collection of 38 units or tools totalling over 1150 PowerPoint slides. Each unit covers a wide range of different delivery and learning styles, offering an exciting way to involve your pupils during lessons or revision sessions. All styles of teaching and learning are supported through use of high quality images, graphics, challenging exercises and questions. Units can be used in the classroom via an interactive whiteboard, data projector or used during individual study via a PC or school network. Science Interactive LTD. PO BOX 50764 LONDON NW6 9AT email: sales@science-interactive.co.uk web: www:science-interactive.co.uk Unit 1: The Digestive System Unit 20: Crude Oil and its Products Unit 2: The Circulatory System Unit 21: Rock Cycle Unit 3: Healthy Body and Immunity Unit 22: Elements, Molecules and Compounds Unit 4: The Respiratory System Unit 23: Ionic and Covalent Compounds Unit 5: Nervous System and the Senses Unit 24: The Halogens, their Uses and Compounds Unit 6: Human Homeostasis Unit 25: The Noble Gases, their Properties and Uses Unit 7: Hormones and the Endocrine System Unit 26: Rates of Reaction Unit 8: Drugs and Bad Body Maintenance Unit 27: Energy Unit 9: Photosynthesis in Green Plants Unit 28: Generating Electricity and its Domestic Use Unit 10: Water Transport in Plants Unit 29: Electricity Unit 11: Flow of Energy and Elements through the Environment Unit 30: Light and the Electromagnetic Spectrum Unit 12: Mitosis and Meiosis Unit 31: Radioactivity Unit 13: Inheritance and Selection Unit 32: Newton's Forces and the Effects of Forces Unit 14: Evolution and Human Impact Unit 33: Earth and Space Unit 15: Genetic Engineering Unit 34: The Earth and Plate Tectonics Unit 16: The Periodic Table and its Elements Unit 35: The Alkaline Earth Metals Unit 17: The Alkali Metals Unit 36: Sound and Hearing Unit 18: Metals and their Properties Unit 37: Natural Forces Unit 19: The Transitional Metals Unit 38: Cells, Tissue, Organs and Organs systems
2. Slide 2: Science Interactive LTD Copyright 2005 Unit 26  Rates of Reaction 
3. Slide 3: Unit 26: Rates of Reaction Science Interactive LTD Copyright 2005 Understand: Keywords: Atoms, Elements, Molecules, Compounds, That atoms and molecules combine to form new 1. products during a chemical reaction. Visual, Signs, Irreversible, Reaction, Types, That all chemical reactions are accompanied by 2. Oxidation, Reduction, Decomposition, visual signs, for example a colour change. Endothermic, Exothermic, Neutralisation, That the rate of a reaction describes how fast a 3. Reaction rates, Substrates, Products, Time, reaction proceeds. Surface area, Concentration, Temperature, That the rate of reaction is measured by 4. Catalysts, Slow, Medium, Fast, Reversible, determining how much product is produced over Ammonia, Haber process & Catalysts. time. Some examples of reactions with either slow or 5. fast rates. That concentration, temperature and surface 6. area and can all affect the rates of reaction. How catalysts can increase the rate of reaction. 7. That all reactions to proceed have to overcome 8. an activation energy. That some reactions are endothermic and some 9. reactions are exothermic. 10. That some reactions are reversible with substrates and products existing in equilibrium. 11. That conditions required for the formation of ammonia during the Haber process. Click mouse to begin Science Interactive LTD PO BOX 50764 LONDON NW6 9AT web: www.science-interactive.co.uk email: sales@science-interactive.co.uk
4. Slide 4: Science Interactive LTD Copyright 2005 Understanding compounds one All materials, compounds or chemicals are made from matter. All materials are made from atoms of elements. There are just over 100 elements in the p_________ table that combine together in different ways to give rise to all the different types of materials that we use and see every day. There are four groups of materials: 1: Elements 2: Metal alloys 3: Ionic Compounds 4: Covalent Compounds Elements, metallic alloys and compounds: Word bank: periodic Elements Metal alloys Ionic compounds Covalent compounds Diagram Notes There are over a 100 An alloy is a mixture of Ionic compounds like Covalent compounds like elements which join two or more different salt contain metal and methane contain non- together to form over 30 metals. Bronze is an non-metal elements. Salt metal elements only. million compounds or alloy and is used in is very important to Methane or natural gas is materials: coins and statues. humans. a fossil fuel: Diamond contains one Bronze contains copper Salt contains sodium and Methane contains type of atom Carbon and tin chlorine. Carbon and Hydrogen
5. Slide 5: Science Interactive LTD Copyright 2005 Understanding compounds two Atoms of elements rarely exist in their pure form, because atoms of elements like to transfer, gain or share electrons. Apart from g_____, oxygen, nitrogen and the Noble gases, most elements are found joined to other elements in compounds. A compound contains two or more different types of a_______ joined together by a chemical bond. These compounds can either be ionic or covalent. Compounds always have a formula which tells us the type and number of atoms they contain. Ionic and covalent compounds: Word bank: gold atoms Sand Water Sodium Chloride Calcium Carbonate SiO2 H2O NaCl CaCO3
6. Slide 6: Science Interactive LTD Copyright 2005 Elements forming new compounds Atoms of elements and small m__________ can combine during a chemical reactions. The new chemicals or compounds produced during a chemical reaction are always totally different. Iron atoms will combine with sulphur atoms when heated to form iron sulphide. How is this different from physical changes in atoms or molecules ? Example Iron (s) + Sulphur (s) Iron Sulphide (s) Fe (s) + S (s) FeS (s) Iron and sulphur reacting to form iron sulphide: Word bank: molecules Iron Sulphur Reaction Iron sulphide Diagram Notes Iron Atoms Sulphur atoms During the reaction Iron sulphide
7. Slide 7: Science Interactive LTD Copyright 2005 Visual signs of chemical change All chemical reactions involve the formation of new products by substrates colliding with one another, breaking bonds, forming new chemical bonds and p________. When substances react, we usually see a visual sign to show us that the reaction is or has taken place. These visual signs are completely absent during p_________ changes where substances either melt, freeze, evaporate or condense. Think about some of the visual signs of chemical change you see in everyday life ? Visual signs of chemical change: Word bank: products physical Colour Smoke Light Sound Heat The type of visual signs that we observe during a chemical reaction range from a change in colour to light and heat energy given off. Some chemical reactions can also give off smoke or even produce a loud noise. All these clues when put together, tells us that a chemical reaction is taking place. Give an example of a reaction that shows the above visual signs ? Colour Smoke Light Sound Heat
8. Slide 8: Science Interactive LTD Copyright 2005 Rates of reaction The rate of a reaction tells us how quickly a chemical reaction, that involves two or more substrates proceeds. The rate of any r________ tells us how quickly the product is formed over time. It also tells us whether a reaction proceeds slowly or violently. This is important, because chemists need to control reactions. If a reaction is too f_____, it may cause an explosion. If it is to slow, it may make the process inefficient and therefore increase production costs. Rates of reaction: Word bank: reaction fast Combustion Explosion Rusting Food spoiling Diagram Notes It is impossible to predict whether two substrates will react and how fast the reaction will proceed. Scientists must perform experiments to observe the behaviour of the reactants during a chemical reaction. These reactions can be over in seconds (e.g. explosions) or take many years (e.g. rusting). Look at the above reactions and determine whether they proceed at a fast, medium or slow rate...Tick the right box ? Fast Medium Slow
9. Slide 9: Science Interactive LTD Copyright 2005 Measuring rates of reactions one There are many different types of reactions in chemistry where substrates combine to form new products. The following reactions and their rates can be monitored using different methods. Remember we must always test to see whether two substrates will r______ with one another and measure their rate of reaction. It is impossible to predict ! Heat (oC) produced over time Colour change over time Mass (g) change over time Volume ( cm3) of gas produced over time Rates of reaction: Word bank: react Heat change Colour change Mass change Volume change Diagram Notes During the combustion In some reactions a As iron rusts, combining In some reactions a gas is of methane, the rate at colour change comes with oxygen and water, it produced or used. You which methane is used with the formation of a gains mass. The rate of can measure the can be monitored by product. A colourimeter the reaction can be respiration rate of an measuring the rate of can measure the rate of monitored by measuring athlete or climber by heat production over colour change over the change in mass over measuring the amount of time. time. time. oxygen used over time.
10. Slide 10: Science Interactive LTD Copyright 2005 Measuring rates of reactions one The rate of a reaction cannot be worked out directly from an equation. This only tells us the molecules that react (substrates) and the molecules that are produced (products) You can determine the rate of reaction by actually performing the e____________ in the laboratory. There are several methods for determining the rate at which the reaction proceeds. These methods include: Colourimeter Mass lost over time Gas volume over time Methods for measuring rates of reaction: Word bank: experiment Colourimeter Mass lost method Volume of a gas Diagram Notes Used when there is a colour Used when there is a change in Used when there is a gas change due to the build up of mass because there is gas produced that can be collected products or the consumption vented off or when a substrate safely using a simple syringe. of substrates. combines with a gas.
11. Slide 11: Science Interactive LTD Copyright 2005 Measuring rates of reactions Mass lost method In reactions involving the formation of a gas as a product, we can measure mass lost over time. As the g____ is produced, it vents off into the atmosphere, reducing the total reaction mass. The electronic balance is able to monitor this loss of m___. Using this method, we can monitor the rate of reaction for a particular reaction. Plotting a graph allows us to work out the rate of reaction (grams of product per second) Mass lost over time: Word bank: gas mass Measuring the mass lost over time Notes Diagram Mass lost (g) Time (seconds) The accurate electronic scales will measure mass lost over time. Notice that at the start of the reaction, the rate is at its quickest, slowing until the graph becomes horizontal. At this point all substrates are used up and the reaction has stopped. Units are in grams. Equation CaCO3 (s) + 2HCl (aq) CaCl2 (aq)+ H2O (l) +C02 (g)
12. Slide 12: Science Interactive LTD Copyright 2005 Measuring rates of reactions Gas volume over time In reactions involving the formation of a gas as a product, we can measure how quickly gas is produced over t______. Using a conical flask and a syringe, the volume of gas produced over time can be recorded. Using this method we can monitor the rate of reaction for a particular reaction. Plotting a g______ allows us to work out the rate of reaction (cm3 of gas per second) Gas volume over time: Word bank: time graph Measuring the volume of a gas produced over time Notes Diagram Gas volume (cm3) Time (seconds) The volume of hydrogen gas was measured over time. Notice that at the start of the reaction the rate is at its quickest, slowing until the graph becomes horizontal. At this point all substrates are used up and the reaction has stopped. Units are in Equation cm3 or dm3. Mg (s) + 2HCl (aq) MgCl2 (aq)+ H2 (g)
13. Slide 13: Science Interactive LTD Copyright 2005 What happens during a reaction one For molecules and atoms to react and produce new products during a chemical reaction they have to first collide into one another. To form new products, old bonds existing between the reacting atoms must be b________ and new bonds must be formed between the atoms forming the new products. Breaking bonds in substrates molecules requires energy. An i__________ source, for example a spark or a heat source provides enough energy to kick start most reactions. Combustion of methane: Word bank: broken ignition Reactants Ignition Midway End CH4 H2O O2 CO2 The combustion of Ignition: Molecules of CH4 and O2 are in the same area. An ignition source provides methane with oxygen the energy to start the reaction. Midway: New products are being formed and energy requires an ignition is released. End: All the substrates have been used up leaving only water (H20) and source like a match. carbon dioxide (CO2) as products.
14. Slide 14: Science Interactive LTD Copyright 2005 What happens during a reaction two Although collision theory is simple and states that for two or more substrates, they must first collide with sufficient energy to react and form new p________, there are right and wrong collisions. Substrates have to c________ with one another in the right way for a successful collision where new products are formed. Look at the examples below. CH4 + 2O2 CO2 + 2H2O Methane + Oxygen Carbon dioxide and water Getting the right collision: Word bank: products collide Unsuccessful Successful Unsuccessful During the combustion of methane with oxygen, not all collisions between the methane molecule and oxygen result in a successful reaction and the formation of new products (carbon dioxide and water.) Only one out of three collision as shown by the diagrams above have the correct orientation, so that the two substrates can react forming new products.
15. Slide 15: Science Interactive LTD Copyright 2005 Factors affecting rates of reaction For atoms or m_________ to react with one another and form new products during a chemical reaction, they have to collide with one another. How often and how hard they collide determines the overall rate of reaction. Collisions of atoms or molecules involved in a chemical reaction are affected by four main factors: Temperature Concentration Particle size Catalysts Factors affecting the rate of reaction: Word bank: molecules Temperature Concentration Particle size Catalysts Reaction temperature Reactant concentration Reactant particle size Presence of catalysts These four factors all affect the number of successful collisions between substrates. These successful collisions lead to the formation of new products. The rate of reaction always needs to be determined experimentally. Remember it cannot be determined by just looking at an equation.
16. Slide 16: Science Interactive LTD Copyright 2005 Rates of reaction Effect of temperature As you increase the temperature of a reaction, the particles have more kinetic energy. This increases the number of times that particles collide and how h______ they crash together, therefore more particles have sufficient energy to break existing bonds before they form new products. In reactions involving e_________, an increase of 10oC usually doubles the reaction rate. In wine or bread making the fermenting yeast sugar solution is always kept warm. Effect of temperature: Word bank: hard enzymes Normal room temperature At 50oC temperature Example Diagram Notes Very few of the particles have At higher temperatures, many Alcohol like wine is sufficient energy when they more of the particles collide more brewed at warm collide that result in a reaction often and have sufficient energy temperatures to increase between the substrate that results in a reaction between the rate at which molecules CH4 and O2. the substrates CH4 and O2. fermentation takes place.
17. Slide 17: Science Interactive LTD Copyright 2005 Rates of reaction Effect of concentration As you increase the concentration of a solution (e.g: acid or alkaline), there are more particles in the same volume of liquid, therefore there is a greater c________ that the particles will collide with each other to form new products. When reacting group II metals like magnesium or calcium with acid, the reaction becomes more vigorous, taking less t______ to finish if you use a higher concentration of acid. Effect of concentration: Word bank: chance time Normal concentration Double concentration Example Diagram Notes The particles in solution move As you increase the concentration, Washing powders use randomly through the solvent. there is a greater chance that the concentration to help These particles can only react particles in solution will collide remove a food stain. when they collide with the and react with the atoms in the Normally you would atoms in the solid. solid. use a double amount.
18. Slide 18: Science Interactive LTD Copyright 2005 Rates of reaction Effect of surface area As you increase the surface area of a solid, by decreasing the size of the particles, you increase the number of particles exposed on the s________ of the solid. These particles can then react with other gases or liquids involved in the chemical reaction. Therefore you increase the number of successful collisions between reacting particles, hence increasing the r_____ of reaction. In fact powders are very dangerous...Did you know that wheat flour or dust can be very explosive ! Effect of surface area: Word bank: surface rate Small surface area Large surface area Example Diagram Notes Only the atoms located on the Here there are many more atoms Fireworks need to be surface can react with the other located on the surface that can explosive, so they use substrates. With a small surface collide and react with other and are packed full of area, fewer collision occur substrates. With a large surface gun powder which between both reactants. area more collisions occur. rapidly releases energy.
19. Slide 19: Science Interactive LTD Copyright 2005 Rates of reaction Effect of gas pressure In reactions involving only gases, if you increase the pressure of the two reacting gases, you have the same number of particles, but in a s________ volume. In other words, increasing the pressure in gases, is just like increasing the concentration in reactions involving solutions. The Haber process which makes ammonia (NH3) from atmospheric nitrogen (N2) and hydrogen (H2) operates at around 200 atmospheres. If the end of the syringe is sealed, how can you increase the pressure of the gases inside the syringe ? Effect of gas pressure: Word bank: smaller Normal atmospheric pressure Twice atmospheric pressure Example 2 atmospheres 1 atmosphere Diagram Notes At normal atmospheric pressure, There are the same number of gas The Haber process the gas molecules are relatively molecules, but in a smaller which makes ammonia spread out and have less chance volume. With more collisions (NH3) from hydrogen of colliding and forming new likely, this increases the chance of and nitrogen uses very products from the reacting a successful collision and therefore high pressures (200 substrates. the rate of reaction. atmospheres)
20. Slide 20: Science Interactive LTD Copyright 2005 Rates of reaction Effective collisions In any reaction, there is a fixed number of substrate molecules able to collide and react to form a fixed number of product molecules. Their kinetic energy follows a typical normal distribution. Those substrate molecules with sufficient k________ energy to collide, break existing bonds and therefore form new p_________ account for only a small number of molecules within the whole population. How factors like temperature, surface area and concentration affect rates is best illustrated by looking at the changes in the kinetic energy of all the substrate molecules. Look at the examples below ! Summary of factors affecting rates of reaction: Word bank: kinetic product Temperature Surface area Concentration Substrates with Substrates with Substrates with Temp 20oC sufficient energy to sufficient energy to sufficient energy to form new products form new products form new products Small particles High concentration Temp 30oC Large particles Low concentration As you increase the temperature of As you increase the surface area of a As you increase the concentration of a a reaction, the particles have more solid, you increase the number of solution (acid or alkaline) there are kinetic energy. This increase the particles exposed on the surface. This more particles in the same volume of number of successful collisions increases the number of successful liquid. This increases the number of between reacting particles or collisions between reacting particles, successful collisions between reacting substrates, therefore increasing the therefore increasing the rate of particles, therefore increasing the rate rate of reaction. reaction. of reaction.
21. Slide 21: Science Interactive LTD Copyright 2005 Rates of reaction Experimental data In a reaction where manganese, copper and zinc metals were reacted with oxygen forming their o_______, the volume of oxygen (cm3) used was recorded over time. A graph was plotted showing the reaction rates for the three metals. Look at the results, experimental set up and the graph and answer the questions ? Experimental data: Word bank: oxides Experimental setup Graph Diagram A graph of volume of O2 (cm3) versus time (s) for the three metals was plotted. Manganese oxide volume of oxygen (cm 3 ) Oxygen Metal Copper oxide Oxygen is passed over the heated metal until Zinc oxide the reaction has finished. Heat source Time (Seconds) 1: Which metal is the most reactive ? Results Time (s) 0 15 30 45 60 75 90 105 120 2: For manganese, which part of the graph Metal/Volume O2 (cm3) represents the fastest reaction rate ? Manganese 0 14 25 33 40 47 52 59 63 3: Which metal is the least reactive ? 4:When does the reaction between Zinc 0 5 9 14 19 23 27 31 35 manganese and oxygen begin to slow down and why ? Copper 0 3 6 9 12 15 17 19 22
22. Slide 22: Science Interactive LTD Copyright 2005 Rates of reaction Effect of catalyst A catalyst is a material which will increase the rate of reaction without be used up. Catalysts are normally transitional metals (Iron, Nickel & Platinum) which are able to lower the activation energy required for new products to form. The reaction takes place on the surface of the catalyst, known as the active site. Effective catalysts are normally in powdered form to help maximise the number of collisions between the reacting substrates and a catalyst’s active site. Usually metals Enzymes are biological catalysts Not used up during the reaction Lower the activation energy Example: The formation of polythene from ethene C2H4 Diagram e then y Pol Catalyst Catalyst active site active site Substrates collide and temporarily bind to the active site on the surface of the catalyst. The bonds in Notes the substrates are weakened by the catalyst. The bonds are broken and the substrates combine with on another to form new products, known as polythene. These new products then leave the active site, allowing the unchanged catalyst to participate in further reactions.
23. Slide 23: Science Interactive LTD Copyright 2005 Rates of reaction Catalysts and enzymes A human body contains many hundreds of different enzymes found inside cells or as part of the digestive system. Without enzymes, which catalyse the breakdown of n_________ like proteins, carbohydrates and fats digestion would be too slow to support all your functions. Like many of the inorganic catalysts, enzymes lower the activation energy and increase the rate of reaction without being used up. With enzymes, the rate of reaction i__________ as the temperature increases, doubling for every 10oC rise in temperature. However, above approximately 40oC, enzymes are denatured or destroyed and will stop working altogether. Name three types of enzymes found in the human gut ? Biological enzymes as catalysts: Word bank: nutrients increases How enzymes speed up the rate of reaction Heat sensitive enzymes With inorganic catalyst Substrates with sufficient energy to form new products Rate of reaction With enzyme With enzyme Without enzyme 0 Temp oC 40 60 80 100 A catalyst will lower the activation required for substrates to react As you increase the temperature by 10oC the with one another to form products. The graph above shows how by rate of reaction doubles until around 40-45oC adding a catalyst the activation energy shifts to the left, increasing the where the high temperature denatures or number of successful collisions and therefore increasing the rate of destroys the enzyme. Inorganic catalysts like reaction. Enzymes are highly specific for their substrate. iron and nickel are not temperature sensitive.
24. Slide 24: Science Interactive LTD Copyright 2005 Using enzymes as catalysts Enzymes are used in a wide variety of industrial applications. Enzymes found in yeast cells are used for fermenting s_______ during alcohol production and making bread. Enzymes found in the bacteria, lactose bacillus are used to produce lactic acid from milk lactose. This is the first step in the production of cheese and dairy yoghurts. Other enzymes are found in modern biological w_________ powders that digest stains on clothing. These modern washing powders work at relatively low temperatures (<40oC) and are energy efficient because you don’t need to use high water temperatures. What temperature would be best to produce cheese from milk ? Biological enzymes as catalysts: Word bank: sugar washing Alcohol Washing powders Bread manufacture Diagram Yeast is an essential bacteria Most washing powders Yeast is used during bread Notes containing enzymes used to contain enzymes that help making. The carbon dioxide gas ferment sugar from grape into with the removal of food produced during the respiration alcohol. Fermentation must be stains. These enzymes digest of wheat sugars and done in an oxygen free and breakdown clothing stains carbohydrates cause the bread environment at temperatures at very low temperatures.... dough to rise. This gives the around 30oC. below 40oC. bread its light texture.
25. Slide 25: Science Interactive LTD Copyright 2005 Useful microbes and enzymes Some bacteria are useful and have been used by humans for many centuries. In the food industry, yeast is used in the manufacture of b______ and alcohol. Many different bacteria, moulds and fungi are used in the manufacture of dairy products like yoghurts and cheeses. Lactose bacillus gives yoghurt its characteristic sharp taste. These m________ and fungi also give blue cheeses, like stilton and roquefort their characteristic flavour, smell and colour. Useful microbes: Word bank: bread moulds Yeast - Bread Yeast - Alcohol Fungi - Cheese Penicillin Diagram Yeast respires glucose Yeast in an oxygen free Mould and fungi are The penicillin mould Notes contained in wheat flour atmosphere is able to added to cheeses and produces a chemical that produces carbon ferment glucose found allowed to grow using that stops the growth of dioxide gas. This causes in grape or grain the nutrients contained many bacteria. It is used the bread to rise. An producing alcohol as a in the milk. Many as an antibiotic to help essential first step in waste product. This is cheeses are produced you fight bacterial making bread. enjoyed by millions of this way. infections. people.
26. Slide 26: Science Interactive LTD Copyright 2005 Energy changes one Chemical changes that happen during a reaction are often accompanied by changes in temperature. This is because e________ is transferred to or from the surroundings during a chemical reaction. Reactions that give out energy to the surroundings like combustion are described as exothermic. Reactions that take in energy from the surroundings like p___________ are described as endothermic. Name five types of endothermic and exothermic reactions ? Examples of energy changes: Word bank: energy photosynthesis Exothermic (Cellular respiration) Endothermic (Photosynthesis) Diagram 6H2O C6H12O6 C6H12O6 6H2O Chloroplast Glucose Mitochondria Energy Energy 6O2 6CO2 6O2 6CO2 Plant cells Cells Notes Cellular respiration releases the chemical Photosynthesis by green plants traps chemical energy found in glucose by, combining with energy in the glucose molecule. Light energy oxygen producing carbon dioxide and water. is used so that water and carbon dioxide This energy is used to support life. molecules can combine to form glucose.
27. Slide 27: Science Interactive LTD Copyright 2005 Energy changes Exothermic Reactions that give out energy to their surroundings in the form of heat, light or sound are called exothermic reactions. These types of reactions are common. An important example of an exothermic reaction is the c_____________ of a fossil fuel like octane, the major component of petrol. During the reaction inside an internal combustion engine, octane is combined with oxygen producing water, carbon dioxide and large amounts of h______ and kinetic energy. Energy changes during exothermic reactions: Word bank: combustion heat Exothermic reactions (Combustion of methane with oxygen) Key O2 CH4 2O2 CH4 Activation energy H2O CO2 Substrates Net heat energy released during reaction In this reaction 2H2O methane (CH4) is combusted with Potential energy CO2 oxygen (O2) to produce water (H2O) Products and CO2 releasing heat energy into the surroundings. Progress of reaction
28. Slide 28: Science Interactive LTD Copyright 2005 Energy changes Endothermic Reactions that take in energy from their surroundings in the form of heat or light are called endothermic reactions. Although these types of reactions are not as common as exothermic reactions, there are several examples. An important example of an endothermic reaction is photosynthesis, whereby l______ energy is used to combine w______ and carbon dioxide forming glucose and oxygen. Energy changes during endothermic reactions: Word bank: light water Endothermic reactions (Photosynthesis in green plants) Key C6H12O6 O2 6O2 C6H12O6 H2O CO2 6H2O 6CO2 Products Activation energy Net energy taken in In this reaction H2O during reaction and CO2 substrates are combined in the Potential energy plant leaf cells using light energy to Substrates produce glucose (C6H12O6) and oxygen (O2) Progress of reaction
29. Slide 29: Science Interactive LTD Copyright 2005 Energy changes Activation energy Most combustion reactions (fuel + oxygen waste gases + energy) require a ‘kick start’ in the form of heat or an ignition spark for the reaction to proceed, even though they are highly exothermic. The energy needed to ‘kick start’ a reaction is called the activation energy. This is a small amount of energy which is required to b______ the bonds of the first few substrate molecules so they can form the reaction products. What allows the reaction to continue is the energy released from the formation of the first few p_________ molecules. Explain why activation energy is a good thing when dealing with fuels like petrol ? Activation energy in reactions: Word bank: break product Example of activation energy (Combustion of methane) Key Energy from a spark or heat source kick starts the reaction CH4 Substrates O2 CH4 Activation energy H2O Molecules with stored chemical energy O2 Net energy released during reaction H2O Potential energy CO2 CO2 Reaction now finishes because products are stable Products Potential energy
30. Slide 30: Science Interactive LTD Copyright 2005 Energy changes Activation energy and catalysts Some reactions proceed very slowly, for example the breakdown of food in the human gut, without enzymes wouldn’t proceed at a sufficient rate to support life. Catalysts are able to speed up reactions without being used up or destroyed during the reaction. Catalysts work by reducing the a__________ energy that is required for a reaction to happen. The reaction takes place on the surface of the catalyst which is called the active site. Effective catalysts are normally in powdered form to help maximise the number of c__________ between the reacting substrates and a catalyst’s active site. Activation energy and catalysts during reactions: Word bank: activation collisions Formation of ammonia from nitrogen and hydrogen Key NH3 3H2 H2 Activation energy A catalyst (iron) reduces without catalyst the energy required to N2 kick start the reaction N2 Activation energy with catalyst NH3 NH3 Potential energy Substrates Products Potential energy
31. Slide 31: Science Interactive LTD Copyright 2005 Everyday reactions one Not all reactions are spectacularly fast or explosive. You already have an idea that reactions involving group I metals (Li, Na & K) proceed relatively quickly. These are good examples of fast reactions. Not all reactions involving metals are fast, some proceed very slowly. Coins made from alloys of tin, copper and silver corrode very slowly. Roman coins buried for centuries show little corrosion. Everyday reactions and energy changes: Corrosion of roman coins Fireworks 10 seconds 2000 years The corrosion of tin, copper or silver coins, Fireworks contain plenty of explosive gunpowder even when buried in wet soil can take many and when lit release large amounts of energy to thousands of years. This is still an example of the surrounding in a very short amount of time. an exothermic process, its just that the release This energy is often used to launch rockets high of energy to the surroundings is so slow it into the sky. What metal ion gives this fire work its deep red colour ? cannot be measured.
32. Slide 32: Science Interactive LTD Copyright 2005 Everyday reactions two During chemical reactions that are exothermic, electrons are either transferred from metals to non-metals or shared between non-metal atoms. This t________ or sharing of electrons increases the stability of ions or atoms in compounds. Some elements like gold are so stable they don’t react, even after many thousands of years. The coins pictured below look exactly the same as when they were fist manufactured, even though they are over 1300 years old. Everyday reactions and energy changes: Word bank: transfer Gold coins Photosynthesis in green plants Summer No reaction ! Gold is found in its natural state in river Photosynthesis by green plants traps chemical deposits or in ‘seams’ in mineral rich deposits. energy in the glucose molecule. Light energy is Gold is so stable that it doesn't combine with used during the summer so that water and carbon any other element and is therefore not found in dioxide can combine to form glucose, which is ionic or covalent compounds. then used by the plant during cellular respiration.
33. Slide 33: Science Interactive LTD Copyright 2005 Everyday reactions three The slow rusting of the Titanic’s iron hull is a perfect example of a reaction that occurs very slowly. Prevention by p__________, for example, of the corrosion of iron which is used to manufacture cars, boats, buildings and bridges costs many billions of pounds. The Eiffel tower in France is painted from top to bottom, all year round at huge cost to stop the structural iron turning into iron oxide or rust. Look at the examples below. Other than painting, how do we prevent iron from rusting ? Everyday reactions and energy changes: Word bank: painting Corrosion and rusting of the titanic Rusting of a car 95 years 20 years The titanic sunk in 1912 with the loss of over Preventing rust by applying oil, paint or a plastic 1000 lives. It has since remained on the ocean coat adds to the coast of making products like floor for over 90 years. This picture shows how cars. We spend many millions of pounds the iron that built her is slowly rusting and protecting products and materials that contain decaying away. iron. What conditions favour rust forming ?
34. Slide 34: Science Interactive LTD Copyright 2005 Reversible reactions one All the reactions that we have studied so far have been one way, where substrates collide and react and then form new products, for example the c___________ of methane with oxygen forms water and carbon dioxide. There exists another type of reaction, a reversible reaction with a forward and back direction. In closed systems (sealed test tube) a reversible reaction will reach equilibrium with both substrate and product molecules present. Look at the examples below ! Reversible reactions: Word bank: combustion Beginning of the reaction Reaction at equilibrium Concentration of products Concentration of substrates Concentration of substrates Concentration of products Concentration of products Substrates Substrates Products Products Time (seconds) Time (seconds) At the beginning of the reversible reaction the When equilibrium is reached, the net concentration of concentration of substrates reduces as the substrates and reactants do not change, however the concentration of the products increases. The rate at forward and back reaction does not stop. The rate for which both substrates and products change both directions is the same. Changing the temperature concentration begins to slow down. or pressure will alter the equilibrium point.
35. Slide 35: Science Interactive LTD Copyright 2005 Reversible reactions two In a closed sealed system containing nitrogen (N2) and hydrogen (H2) molecules, an equilibrium would be reached where ammonia (NH3) and the two substrate molecules nitrogen and hydrogen would also be present. At equilibrium, you might think that the reaction has finished but this is not the case. Some H2 and N2 molecules are still reacting to give NH3, but they are compensated by NH3 molecules reacting to form H2 and N2. Look at the example below. Reversible reactions: N2 3H2 2NH3 N2 + 3H2 forward backward Concentration of substrates Products Concentration of products The reaction will reach equilibrium where Substrates all three molecules (N2 H2 + NH3) exist. NH3 Time (minutes) The substrates nitrogen and hydrogen (N2 + H2) react to form ammonia (NH3) until an equilibrium is reached where all three molecules are present. At equilibrium, the reaction continues in the forward and backward direction. The net amount of substrates and products remains the same because the rate of ammonia being produced and reverting back to the substrates hydrogen and nitrogen is the same.
36. Slide 36: Science Interactive LTD Copyright 2005 The Haber process one Modern agriculture that produces all the foodstuffs for human consumption, relies on millions of tonnes of fertiliser. These fertilisers supply crops with all the m_________ that they need for healthy growth and development. Plants cannot obtain their nitrogen directly from the atmosphere, it must be in the soluble form nitrate (NO3-) Fertilisers are rich in the nitrate ion. Ammonia which is used to make nitric acid (HNO3) is made by reacting n_________ and hydrogen. This reaction is very slow and reversible i.e. some of the ammonia that is formed breaks down again to form hydrogen and nitrogen. The first attempts, in the late 1800s to make ammonia only yielded very small amounts. 3H2 + N2 2NH3 Production of ammonia: The Haber process: Word bank: minerals nitrogen Overview of the Haber equation Crops and fertilisers N2 3H2 Concentration of substrates Concentration of products Products Substrates NH3 N2 NH3 3H2 Time (minutes) The five main crops (wheat, rice, Production of ammonia for fertilisers is vital for modern farming. 100 years ago, very small amounts were produced until Fritz Haber began to use his corn, potato and sugar) are grown knowledge of collision theory, reversible reactions and catalysts to improve using fertilisers to enrich the soil. yields.
37. Slide 37: Science Interactive LTD Copyright 2005 The Haber process two The first attempts to make ammonia from nitrogen and hydrogen only yielded very small amounts. Fritz Haber began to study how to improve the y______ of ammonia just as Europe’s population began to explode. He succeeded by using his knowledge of collision theory and understanding how catalysts work. He discovered the main factors that controlled the yield of ammonia (NH3), which was then used to make fertilisers. These are temperature, pressure and the presence of an iron catalyst. Because of Fritz Haber, modern agriculture is now able to feed all those millions of people who live in the USA and Europe. The Haber process: Word bank: yield Temperature Pressure Catalyst 70 70 70 350oC 300atms % yield of ammonia % yield of ammonia % yield of ammonia 400oC 200atms Catalyst 450oC lyst cata 150atms t hou Wit 550oC 100atms 0 Pressure (atms) 200 400 0 Temp (oC) 300 600 Time (minutes) Heating increases the rate of Increasing the pressure increases the Haber also discovered that the surface of reaction between hydrogen and rate and the yield. When the iron binds both nitrogen and hydrogen nitrogen. Because the reaction is reaction goes in the forward and reduces the amount of energy that is endothermic and reversible, direction 4 molecules (N2 & 3H2) required to break the nitrogen-nitrogen heating can lower the overall yield bond. Nitrogen atoms are held to one produce only 2 molecules of of ammonia. It forces the reaction another by a triple bond. The iron ammonia. Therefore increasing the in the backwards direction. catalyst is not directly involved in the pressure forces the reaction in the reaction. forward direction.
38. Slide 38: Science Interactive LTD Copyright 2005 The Haber process three Haber realised, using basic theory, that low temperatures and high pressures would be the right conditions for the highest yield of ammonia, however, the reaction in the forward direction was too slow to be profitable. He came up with the solution of using moderately high temperatures and pressures with an i_____ catalyst. Although the reaction still didn’t go to completion, the yield of ammonia was high enough. He also helped the reaction go in the forward direction by cooling and removing the liquid a__________ by using a condenser at -33oC. He also recycled the unused nitrogen and hydrogen so they could go through the main reactor until they had formed ammonia. The Haber process: Word bank: iron ammonia Nitrogen Notes Hydrogen Compressor 200atm 1:Hydrogen from methane and nitrogen from air are heated in the reforming vessel. Oxygen in the 400oC air is removed by reacting it with hydrogen to form water. The ratio Reformer of hydrogen to nitrogen is 3:1. 2: The compressor increases the pressure to about 200 atmospheres. 3: The reaction between hydrogen Reactor vessel and nitrogen occurs on the surface Haber process of the iron catalyst. N2 + 3H2 2NH3 4: The ammonia is cooled and removed as a liquid in the Condenser forward condenser. Nitrogen and hydrogen Ammonia are recycled via the compressor. backward
39. Slide 39: Science Interactive LTD Copyright 2005 Extension questions and homework 1: Define the following terms: Substrates, Products, Endothermic, Exothermic, Reaction-rates & Collision theory. 2: Look at the three pictures below. Complete the table. Picture Process Exothermic ? Endothermic ? Reversible ? One Photosynthesis Two Rusting Three Decomposition 3: Answer the following: a) Place the following metals in order of their reactivity, starting with the most reactive. Design an experiment that would show you how reactive each metal was. Metals react with hydrochloric acid to produce hydrogen gas and heat. Magnesium: Lithium: Sodium: Zinc: Potassium: Gold: Calcium: & Silver: b) What is a catalyst and give 2 examples of catalysts explaining how each one functions. c) What are the four factors that affect the rate of reaction between two substrates. d) Hydrogen peroxide (2H2O2 2H20 + O2) will decompose to form oxygen and water. The reaction is catalysed by some transitional metal oxides. You are given oxides of copper, manganese and nickel. How would you determine which metal oxide is the best catalyst.
40. Slide 40: Science Interactive LTD Copyright 2005 4: Use the following word to answer question 4a to 4f. Size of particle Concentration Fast Medium Slow Collision Products Reactants a) Powders have a large _____________. b) Molecules or atoms do this during a chemical reaction. c) Rusting iron is an example of a ___________ reaction. d) A firework going off is an example of a ____________ reaction. e) When you add more washing powder to a wash you increase the ____________ of washing powder. f) Digestion of food molecules by enzymes is an example of a _____________ reaction. 5: The table below shows how much ammonia is produced using different conditions. Pressure (atm) /Temp oC 350oC 450oC 550oC From the values in the table what happens to the yield of ammonia as: (a) The temperature is increased. (b) The pressure 50 39.5% 34.5% 10.6% is increased. (c) Using your ideas about colliding particles, 100 52.3% 45.3% 18.4% explain how the rate of the reaction will change as the 200 66.8% 54.8% 24.9% temperature increases. 400 79.5% 67.5% 31.4% 6: Place these reaction examples in order of their rate. Reaction Rusting Digestion Combustion of methane Silver tarnishing Gun powder explosion Order Internet: Go to google.co.uk and find out about the use of catalysts like enzymes found in the human body. How do they help the breakdown of proteins, fats and carbohydrates. Compare these enzymes to those found in biological washing powders. Why can they only used in a cool wash below 40oC.