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Mastering Rates of Reaction: Experiments and Insights

Discover the intricacies of fast and slow reactions, measurement techniques, and factors influencing reaction rates. Learn through interactive experiments and explore collision theory.

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Mastering Rates of Reaction: Experiments and Insights

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  1. Unit 1 Rates of reaction

  2. Contents • Fast and slow reactions • Measuring the rate • Experiments • Factors influencing the rates of reaction • Collision theory • Testing and assessment PROGETTO CLIL

  3. Reactions at different rates • There are chemical reactions that occur very slowly and others that occur very quickly. Rust formation Fireworks Exercise 1 PROGETTO CLIL

  4. Control rates Being able to control the speed of chemical reactions is important both in everyday life (for example in cooking) and when making new materials on an industrial scale. PROGETTO CLIL

  5. Rates and time • If a reaction takes longer, its rate decreases. • Rate of reaction  1/time PROGETTO CLIL

  6. Measuring rates The only way we can find out about the rate of a particular reaction is to carry out an experiment.A balanced equation for the reaction tells us nothing about its rate. We need to have some ways of measuring: • either the rate at which reactants are usedup in a reaction • or the rate at which products are formed in a reaction. The practical methods which can be used are various: PROGETTO CLIL

  7. Mass loss method The rate of a reaction that produces a gas can be measured by following the mass loss as the gas escapes from the reaction flask. For example we can measure the loss of mass in this reaction: CaCO3(s) + 2 HCl(aq) CaCl2(aq) + H2O(l) + CO2(g) A gas is produced when calcium carbonate reacts with hydrochloric acid. PROGETTO CLIL

  8. …other methods Measuring: • colour change • volume of gas evolved • formation of precipitate PROGETTO CLIL

  9. Experiments Tasks First phase You will work in groups. Each group will carry out an experiment. In each group there will be: workers, observers and one speaker. • The workers have to manage the experiment as described in the guide. • The observers have to observe and write down the experimental data. • All the components contribute to complete the exercises and the “guided report”. Second phase • The speaker of each group reads the completed guided report to the whole class. • The other students, while listening to the speaker, complete the “guided reports”. • After that there will be few minutes for the checking. PROGETTO CLIL

  10. Equipment Glass tubing Test tube stand PROGETTO CLIL

  11. Safety • Wear chemical splash goggles for the acidic solutions. • Normal laboratory care is needed. PROGETTO CLIL

  12. Experiments • Measuring rate • Nature of reactants • Concentration • Surface area • Temperature • Catalysts PROGETTO CLIL

  13. And now….. Everybody in the chemistry lab……… have fun!!!!! PROGETTO CLIL

  14. Back from the lab….. • What have we learned through the experiments? Summarizing... PROGETTO CLIL

  15. Concentration Pressure Factors affecting rate of reaction Stirring Particle size Catalysts Temperature Nature of reactants PROGETTO CLIL

  16. Results The speed (rate) of chemical reactions increases : • if the temperature increases; • if the reactants are in ionic form; • if the concentration of dissolved reactants or the pressure of gases increases; • if solid reactants are in smaller pieces (greater surface area); • if a catalyst is used. Exercise 2 PROGETTO CLIL

  17. Theory of collisions • In order to react molecules and atoms must touch each other. • In a gas or liquid phase, this generally happens when the reactant molecules collide. • They must hit each other hard enough to react. • If they collide and are in the right position, they can form a chemical bond. PROGETTO CLIL

  18. example 1 ….. PROGETTO CLIL

  19. ….. its energetic profile PROGETTO CLIL

  20. example 2 …….. PROGETTO CLIL

  21. ……its energetic profile The exothermic reaction is represented by the following graph. PROGETTO CLIL

  22. Example 3….water formation Reactants Energy Products Reaction coordinate PROGETTO CLIL

  23. Theory of collisions and factors affecting a reaction • Collision frequency: more collisions mean more chances to form bonds. • Collision energy: higher energy makes bonds break; the chance of new bond forming increases. • Collision geometry: molecules must face the right direction. Exercise 4 PROGETTO CLIL

  24. Concentration • If there is more concentration of a substance in a system the chance that molecules will collide is higher and the rate of the reaction speeds up. • If there is less concentration of reactants there will be fewer collisions and the reaction will probably happen at a slower speed. PROGETTO CLIL

  25. Pressure • In reactions with gases , the number of particles is increased by pressing them. • Then increasing the pressure, the rate of reaction increases. PROGETTO CLIL

  26. Surface area • Smaller particles  faster reaction. • Smallest particles possible are molecules or ions. • Dissolving reactants speed up reactions. • When two solids react with each other the reaction is slow. • Molecules can only collide at the surface. • Smaller particles bigger surface area. PROGETTO CLIL

  27. Effects of stirring Stirring the reactants is an important rate factor: if the reacting mixture is not stirred the reactant concentration in solution becomes much less near the solid as it tends to settle out. PROGETTO CLIL

  28. Effects of temperature • Chemical reactions can only occur when reacting particles collide with each other and with sufficient energy. • Activation energy is the minimum amount of energy particles must have to react. • Increasing the temperature increases the speed of the reacting particles so that they collide more frequently and more energetically.This increases the rate of reaction. PROGETTO CLIL

  29. Activation energy • The minimum amount of energy needed for initiating a chemical reaction is the activation energy (Ea). • This is different according to the type of bonds of the reactants. • Colliding reactant molecules possess kinetic energy > the activation energy or Ea. PROGETTO CLIL

  30. Activation energy - example Activated Complex or Transition State Activation Energy Reactants Energy Products Reaction coordinate PROGETTO CLIL

  31. Activated Complex or Transition State Reactants Energy Products Reaction coordinate PROGETTO CLIL

  32. Activated complex PROGETTO CLIL

  33. Activated complex The species temporarily formed by the reactant molecules are called activated complex.The concentration of the activated complex is extremely small. PROGETTO CLIL

  34. Activation energy decrease • Suppose you have a mountain between two valleys so that the only way for people to get from one valley to the other is over the mountain. • Now suppose a tunnel is cut through the mountain. Many more people will now manage to get from one valley to the other by this easier route. • You could say that the tunnel route has a lower activation energy than going over the mountain. PROGETTO CLIL

  35. Catalysts Substances that: • speed up a reaction without being used up. • Speed up a reaction by giving the reaction a new path. The new path has a lower activation energy and more molecules have this energy. The reaction goes faster. • Inhibitors: substances that block catalysts.Exercise 5 (only pc) PROGETTO CLIL

  36. Use of catalysts • Increasing the rates of chemical reactions is important in industry because it helps to reduce costs. • Catalysts increase the rate of a reaction by helping break chemical bonds in reactant molecules. Catalyst silencer of a car PROGETTO CLIL

  37. Concentration Reactants Energy Products Reaction coordinate PROGETTO CLIL

  38. Enzymes • Enzymes are catalysts. Most are proteins. Enzymes bind temporarily to one or more of the reactants of the reaction they catalyze. In doing so, they lower the amount of activation energy needed and thus speed up the reaction. Examples: • Catalase. It catalyzes the decomposition of hydrogen peroxide into water and oxygen. 2H2O2 2H2O + O2 One molecule of catalase can break 40 million molecules of hydrogen peroxide each second. PROGETTO CLIL

  39. Example Enzymes are used to make some soft-centred chocolates. An enzyme called invertase will convert a sugar called sucrose into smaller sugar molecules called glucose and fructose. The breaking down of some sucrose moleculescauses the chocolate to become softer and sweeter (fructose is particularly sweet). PROGETTO CLIL

  40. Revise the whole topic and don't forget the glossary ! Glossary PROGETTO CLIL

  41. Finally ....testing... PROGETTO CLIL

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