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C3 Contents

C3 Contents

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C3 Contents

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  1. How to Operate This PowerPoint Select slideshow and click on “From Beginning”. Click once and this box will disappear, then choose the section you wish to look at and click on next to it. C3 Contents Reaction Times and Rates Rates and Conditions Explosions and Catalysts Reacting Masses Percentage Yield And Atom Economy Energy Batch or Continuous Allotropes and Nanochemistry

  2. C3: Chemical Economics Reaction Times and Rates Learning Objectives All: Be able to recall different examples of reactions Most: Be able to compare different reaction rates Some: Be able to interpret reaction rate data Starter:List 10 different chemical reactions e.g. rusting

  3. What is a reaction? • A reaction is when the reactants are converted into products • This happens when reactant particles collide with each other • Reactions can be fast or slow • Look at your list of reactions and sort them into fast or slow reactions • Rusting is an example of a slow reaction • Explosions are fast reactions

  4. Explosions • Explosions are fast reactions • For your exam you will need to remember several different types of explosion • Examples include burning hydrogen TNT/dynamite Custard powder or flour

  5. Rates • A rate is a measure of change in a single unit of time • The rate of reaction measures how much product is produced in a specified time period • Units of rates of reaction are often things like g/s, g/min, cm3/s, cm3/min • They vary depending on the reaction – you use the most appropriate for the amount of product produced in that time • e.g. 0.5g/min is the same as 0.00833g/s but it is much more sensible to use 0.5g/min

  6. Measuring Rates of Reaction • There are several ways to measure the rate of a reaction • The volume of gas given off – the gas can either be collected in an upturned measuring cylinder full of water or in a special gas syringe, you then dived the amount by time taken to get the reaction rate • The mass of product given off – by working out how much the mass of the reactants alters and dividing it by the time taken • The disappearing cross – a cross is marked on paper underneath the flask or beaker and you time how long it is until the cross is no longer visible

  7. Ending the Reaction • A reaction stops when no more product is produced • This is when all of one of the reactants has been converted into product • This reactant is called the limiting reactant • At the end of a reaction you have the product plus any of the reactants that were in excess • The time it takes for the reaction to finish and the amount of product created depends on the amount (the number of particles) of the reactants

  8. Limiting Reactants • The amount of product made in a reaction is directly proportional to the amount of limiting reactant used • This is because once all of the limiting reactant has been used the reaction has to stop (unless more is added) • If you plotted this on a graph it would be a straight line with a positive gradient and pass through the origin • This is about the amount of product and reactant, not the rate of the reaction

  9. Practical • Follow the instructions given to investigate the rate of a reaction • Don’t forget to write it up: • Make sure you produce a graph from your results Aim Hypothesis Equipment Method Diagram Results, graph and data analysis Conclusion (linked to hypothesis) Evaluation

  10. Interpreting Reaction Rate Data • The rate of a reaction is not normally constant – it changes throughout the experiment • There are various ways to calculate the reaction rate at any moment in time • Reading it off a graph (not very specific) • Comparing gradients – the steeper the gradient, the faster the reaction • Time taken for reaction to stop (line on graph to level off) – quicker the reaction stops, the faster the reaction

  11. Interpreting Reaction Rate Data • For specific information you can work out the actual rate of reaction at any point in time by calculating the gradient • Draw a line at tangent to the curve, showing what the gradient is at that point • Calculate the change in amount of product produced • Divide it by the change in time and you will get the gradient of the line – this is your reaction rate at that specific point • Remember UNITS!

  12. C3: Chemical Economics Reaction Rates and Changing Conditions Learning Objectives All: Be able to recall what can affect the rate of a reaction Most: Be able to relate reaction rate to collision theory Some: Be able to hypothesise how the rate of reaction will change under certain conditions Starter:Draw a 3 x 3 grid in your book

  13. Bingo Choose 9 of these keywords to write into your table Rusting Size Reaction Rate Pressure g/s Mass Gas Gas Syringe Measuring Cylinder Activation Energy Successful Collision Products Explosion Reactants Units Limiting Reactant Collision Theory Disappearing Cross Gradient

  14. Collision Theory • For a reaction to occur the reactant particles need to collide • If they do not collide with enough energy then the reaction will not occur • If they have enough energy for a successful collision then there will be a reaction • This level of energy is called the activation energy

  15. Collision Theory • The rate of reaction depends on the number of successful collisions between reacting particles • The more often the particles collide, the faster the reaction • The more energy transferred the greater the chance that the collision will be successful • Can you think of 4 things that could affect the frequency of successful collisions

  16. Pressure • How do you think pressure affects the rate of reaction? • The higher the pressure, the greater the rate of reaction • The particles have a smaller space to move in and so collide more often • By colliding more often there is a greater chance of the collisions being successful

  17. Concentration • How do you think concentration affects the rate of reaction? • The higher the concentration, the greater the rate of reaction • By increasing the number of reactant particles in the same space they collide more often • By colliding more often there is a greater chance of the collisions being successful

  18. Practical • Follow the instructions given to investigate how concentration affects the rate of a reaction • Don’t forget to write it up: • Make sure you produce a graph from your results Aim Hypothesis Equipment Method Diagram Results, graph and data analysis Conclusion (linked to hypothesis) Evaluation

  19. Practical • Follow the instructions given to investigate how concentration affects the rate of a reaction • Don’t forget to write it up: • Make sure you produce a graph from your results Aim Hypothesis Equipment Method Diagram Results, graph and data analysis Conclusion (linked to hypothesis) Evaluation

  20. Temperature • How do you think temperature affects the rate of reaction? • The higher the temperature, the greater the rate of reaction • By increasing the amount of kinetic energy the reactant particles have the more often they will collide and the more often they will collide successfully

  21. C3: Chemical Economics Explosions and Catalysts Learning Objectives All: Be able to recall affect of surface area on rate of reaction Most: Be able to explain the importance of catalysts Some: Be able to interpret data relating rate of reaction to conditions Starter: What conditions can affect the rate of a reaction?

  22. Surface Area • The surface area of an substance can be altered without changing the amount of substance present • By cutting the substance into smaller pieces or by grinding it into a powder you increase the surface area

  23. Surface Area • How do you think surface affects the rate of reaction? • The greater the surface area, the greater the rate of reaction • The particles are more exposed to other reactants, so collisions can happen more often • By colliding more often there is a greater chance of the collisions being successful

  24. Powder Danger • Even the most innocuous powder can be dangerous (eg flour, custard powder, sulphur, sugar) • Powder that is very fine can float in the air, where it has access to plenty of oxygen • If the powder is ignited then there can be an explosion • Explosion: a very fast reaction that produces a large volume of gaseous products which move outwards from the reaction at high speed creating an explosive effect

  25. Practical • Follow the instructions given to investigate how concentration affects the rate of a reaction • Don’t forget to write it up: • Make sure you produce a graph from your results Aim Hypothesis Equipment Method Diagram Results, graph and data analysis Conclusion (linked to hypothesis) Evaluation

  26. Catalyst • A catalyst is something that speeds up the rate of reaction • The catalyst does not change the amount of product created, not the amount of reactant needed • A catalyst is unchanged by the reaction – it accelerates the reaction but is not affected by it • The amount of catalyst at the beginning and end of a reaction is the same

  27. Catalyst • A catalyst speeds up the reaction without being altered itself • Only a small amount of catalyst is needed to catalyse large amount of reactants • Catalysts do not speed up the number of collisions in a reaction – they increase the number of successful collisions With Catalyst Without Catalyst Amount of Product Time

  28. Catalysts and Collisions • Catalysts increase the frequency of successful collisions • They do this by helping particles collide with the correct orientation or by reducing the activation energy needed for a successful collision • Most catalysts are very specific – they will only work for one reaction

  29. Rates of Reaction • What can affect the rate of a reaction? How many things can you name? (There are at least 5 answers) • Pressure • Concentration • Temperature • Surface Area • Presence of a catalyst • How do they do this? – Think about collision theory • The increase the number of successful collisions which decreases the time it takes for all of the limiting reactant to react

  30. C3: Chemical Economics Reacting Masses Learning Objectives All: Be able to explain what relative atomic mass is Most: Be able to understand the principle of conserving mass Some: Be able to calculate product masses Starter:What is a) an atom? b) an element? c) a molecule? d) a compound? e) a mixture

  31. Relative Atomic Mass • Atoms of different elements are different sizes and different weights • The further along the periodic table you get the larger and heavier the atoms get • Even so one atom is very small – one carbon atom is approx. 0.00000000000000000000001992g • Because they are so small we use a comparative scale – as a result there are no units • Hydrogen is the smallest atom so we say that it weighs 1 C 12 6

  32. Relative Atomic Mass • The periodic table tells you what the atomic mass of each element • The largest of the two numbers on an element is the relative atomic mass of one atom of that element • Some of the most common RAM are: Hydrogen – 1 Carbon - 12 Nitrogen – 14 Oxygen – 16 O 16 8 • Originally everything was compared to the mass of hydrogen, now it is compared to 1/12th of carbon (essentially the same thing)

  33. Relative Formula Mass • Using the RAM you can also calculate the Relative Formula Mass (Mr) • A hydrogen molecule has the formula H2 so H + H = 1 + 1 = 2 • The formula of an oxygen molecule is O2 so 16 + 16 = 32 • Water has the formula H2O so it has the RFM of 1 + 1 + 16 = 18 • Remember there are no units because it is a relative scale

  34. Relative Formula Mass • Methane is CH4, what is its RFM? • C = 12, H = 1, CH4 = 12 + 4 x 1 = 12 + 4 = 16 • Sulphuric acid is H2SO4, what is its RFM? • H = 1, S = 32, O = 16 H2SO4 = 2 x 1 + 32 + 4 x 16 H2SO4 = 2 + 32 + 64 = 98 • What is the RFM of Al(OH)3? • Al = 27, O = 16, H = 1 • Al(OH)3 = 27 + 3(16 + 1) • Al(OH)3= 27 + 3 x 17 • Al(OH)3 = 27 + 51 • Al(OH)3 = 78

  35. Conservation of Mass • The total mass in a reaction does not change – the total mass of the products will equal the total mass of the reactants – atoms do not vanish • If the mass seems to decrease then it has probably given off a gas and lost atoms that way • If the mass seems to increase then some of the reactants have probably reacted with a gas in the atmosphere – usually oxygen

  36. Conserving Mass • By looking at the equation for the reaction you can see if mass is conserved • For example when CaCO3 decomposes this is the equation • What is the RFM of the reactant? • CaCO3 = 40 + 12 + 3x16 = 100 • What is the RFM of each of the products? • CaO = 40 + 16 = 56 • CO2 = 12 + 2x16 = 44 • What is the total RFM of the products? • CaO + CO2 = 56 + 44 = 100 CaCO3CaO + CO2

  37. Practical Instructions • Measure 10cm3 Sodium Hydroxide into beaker A using measuring cylinder • Weigh beaker A and record weight • Measure 10cm3 Copper Sulphate into beaker B using measuring cylinder • Weigh beaker B and record weight • Add contents of beaker A to beaker B • Weigh both beakers together and record weight • Weigh dry filter paper and record weight • Filter contents of beaker B • Reweigh filter paper when dry and record weight

  38. Practical Results • How successful was your experiment? How much product do you have? How much mass should be in the liquid? Why do you think you got as little product as you did? How could you make your experiment more precise? More accurate?

  39. Predicting Products • It is possible to predict how much of each product will be made by looking at the equation for the reaction • How much CO2 is made when 500g of CaCO3 decomposes? • What is the RFM of CaCO3? • 40 + 12 + 3x16 = 100 • What is the RFM of CO2? • 12 + 2x16 = 44 • So 100g of CaCO3 gives 44g of CO2 • Therefore 500g of CaCO3 gives 5x44 of CO2 • 500g of CaCO3 gives 220g of CO2 CaCO3CaO + CO2

  40. Predicting Products • How much water is made when 340g of hydrogen peroxide decomposes? • Hydrogen peroxide - H2O2 Water - H2O • What is the RFM of H2O2? • 2x1 + 2x16 = 2 + 32 = 34 • What is the RFM of H2O? • 2x1 + 16 = 2 + 16 = 18 • So 34g of H2O2 gives 18g of H2O • Therefore 340g of H2O2 gives 10x18 of H2O • 340g of H2O2 gives 180g of H2O

  41. Predicting Products • In reality reactions do not produce as much product as calculated – this could be for a variety of reasons • If it is a reversible reaction the reaction might not go all the way to completion • Some of the product might be lost when it is removed • Some of the reactants might react in an unexpected way • Remember the reaction (and the amount of product produced) is controlled by the amount of limiting reactant

  42. Predicting Products • Remember that the amount of product made is directly proportional to the amount of limiting reagent • In your exam you might be asked to work out how much of a specific product is made when an certain amount of one reactant reacts with an excess of another • You can do this by calculating the ratio of reactant to product • Example: What mass of sodium chloride is produced when 5.3g of sodium carbonate reacts with an excess of hydrochloric acid?

  43. Working With Ratios • Example: What mass of sodium chloride is produced when 5.3g of sodium carbonate reacts with an excess of hydrochloric acid? • Na2CO3 + 2HCl → 2NaCl + H2O + CO2 • What is the Mr of Na2CO3? • 2x23 + 12 + 3x16 = 46 + 12 + 48 = 106 • What is the Mr of 2NaCl? • 2(23 + 35.5) = 2(58.5) = 117 • Ratio of NaCl to Na2CO3 is 117 ÷ 106 = 1.103773585 • Mass of NaCl formed 5.3 x (117 ÷ 106) = 5.3 x 1.103773585 • Mass of NaCl formed from 5.3g of Na2CO3 = 5.85g

  44. C3: Chemical Economics Percentage Yield and Atom Economy Learning Objectives All: Be able to explain what is meant by percentage yield and atom economy Most: Be able to calculate percentage yield and atom economy Some: Be able to hypothesise why there is a difference between theoretical and actual figures Starter:Decipher the code you have been given

  45. Percentage Yield • The percentage yield is a way of comparing the amount of product made with the amount predicted • We refer to the amount of product made as actual yield Percentage Yield = Actual Yield (g) f x 100 (%) Predicted Yield (g) • 100% yield means that there is no loss of product, 0% yield means that there is no product made

  46. Percentage Yield • The percentage yield will always be less than 100% • Product can be lost in filtration, evaporation, transferring liquids or heating • Another reason for the yield to be low is the possibility that not all of the reactant has reacted and changed into product (especially if it is a reversible reaction

  47. Industrial Yield • In industry it is important to have as high a yield as possible • Having a high yield reduces the amount of reactants wasted • Having a high yield also reduces the process more profitable and reduces costs

  48. Atom Economy • Percentage yield was a way to compare the mass of product actually produced with the mass that should have been produced • Atom economy is a way to compare the mass of useful product produced with the total mass of product produced, and so work out what percentage of atoms are wasted • In an ideal world all of the reactants would be converted into the product that you wanted • However most reactions produce unwanted by-products

  49. Atom Economy • If only the useful product is created the atom economy will be 100% • Example find the atom economy of making Hydrogen from this: Zn + 2HCl → ZnCl2 + H2 • Mr of H2 = 2x1 = 2 • Mr of ZnCl2 = 65 + 2x35.5 = 136 • Mr of all products = 2 + 136 = 138 • Atom Economy = (2 ÷ 138) x 100 • AE = 0.0145 x 100 = 1.45% Atom Economy = Mr of useful product x 100 (%) Mr of all products

  50. Atom Economy • If an industrial reaction has a high atom economy the process is more cost efficient, so more profit is made • An industrial reaction with a high atom economy is also more sustainable as it uses fewer resources and produces less waste • As a result the higher the atom economy is, the better it is for the environment