Chemical Reactions

1. Chemical Reactions 1. Recognising a Reaction LO: I understand what a chemical reaction is.

19. When a chemical reaction takes place a .substance is always formed. new Examples of chemical reactions: • C. ooking urning • B. • C (rusting) orrosion rowing • G. ecaying • D. LO: I understand what a chemical reaction is.

20. If a new substance isn’t made then a change has happened. physical Examples of physical changes: elting • M. reezing • F. ondensing • C. oiling vaporating • B/e. issolving • D. reaking • B. LO: I understand what a chemical reaction is.

21. 2. Evidence for a Chemical Reaction LO: I know some indicators of a chemical reaction.

22. (a) Change in Appearance Aim: To show that a change in appearance can occur during a chemical reaction. Diagram: filter paper potassium iodide lead nitrate filter funnel + LO: I know some indicators of a chemical reaction.

23. Method: 1. Potassium iodide solution and lead nitrate solution was added to separate test tubes. 2. One solution was poured into the other. 3. The mixture was filtered. Result: A yellow solid was produced. Conclusion: During the reaction the two colourless solutions changed appearance to give a yellow solid. LO: I know some indicators of a chemical reaction.

24. (b) Change in Energy Aim: To show that some chemical reactions can produce a change in temperature. Diagram: thermometer iron copper sulphate solution LO: I know some indicators of a chemical reaction.

25. 1. The temperature of the copper sulphate solution was measured. Method: 2. Two spatulas of iron filings were added to the boiling tube and stirred. 3. The highest temperature reached was measured. Result: Start Temperature = Final Temperature = Temperature Rise = Conclusion: During the reaction the temperature increased due to heat energy being produced. LO: I know some indicators of a chemical reaction.

26. Change in Energy (continued) Aim: To show that some chemical reactions can produce light energy. Diagram: magnesium Bunsen LO: I know some indicators of a chemical reaction.

27. Method: 1. A small strip of magnesium was held in a Bunsen flame at the tip of the cone. 2. The magnesium was pulled out of the flame once it caught fire. Result: The magnesium burned with a bright white light. Conclusion: The bright white light during the reaction shows that light energy was produced. LO: I know some indicators of a chemical reaction.

28. Summary During a chemical reaction some of the following may be seen (observed): • A change in appearance ( change) colour light sound heat • A change in energy (, or ) • A new substance is formed ( or ) solid gas LO: I know some indicators of a chemical reaction.

29. 3. Chemical Equations LO: I know how to write a chemical equation.

30. A chemical equation is a short way of writing what happens during a chemical reaction. For example: Magnesium burns in oxygen to produce magnesium oxide. Equation: magnesium oxide + magnesium oxygen reactants product (always on the left) (always on the right) LO: I know how to write a chemical equation.

31. Examples: Zinc metals reacts with oxygen to produce zinc oxide. Hydrogen gas reacts with chlorine gas to produce hydrogen chloride gas. hydrogen chloride hydrogen Copper sulphate reacts with iron to produce iron sulphate and copper. + chlorine carbon dioxide iron sulphate lead iodide potassium nitrate water copper potassium iodide methane copper sulphate lead nitrate + + + + + + iron oxygen Potassium iodide and lead nitrate solutions react to produce lead iodide and potassium nitrate. zinc oxide zinc + oxygen Methane gas reacts with oxygen to produce carbon dioxide and water. LO: I know how to write a chemical equation.

32. 4. Speed of Reactions LO: I know how to change the speed of a chemical reaction.

33. (a) Change in Particle Size Aim: To show the effect of changing the particle size on the speed of a reaction. Diagram: potassium permanganate rhubarb 1 piece 8 pieces (large particles) (small particles) LO: I know how particle size affects the speed of reaction.

34. Method: 1. 50cm3 of potassium permanganate was added to two beakers. 2. A piece of rhubarb was added to one beaker. 3. An identical piece of rhubarb was chopped into 8 pieces and added to the other beaker. 4. Both beakers were stirred. Result: The beaker with the small pieces went colourless first. Conclusion: The smaller the particle size, the faster the speed of the reaction. LO: I know how particle size affects the speed of a reaction.

35. Everyday examples: faster Potatoes cook when cut up into smaller pieces. slower A block of wood burns than wood shavings. explosive Coal dust is whereas a lump isn’t. burn Steel wool can but a steel nail can’t. LO: I know how particle size affects the speed of a reaction.

36. (b) Change in Temperature Aim: To show the effect of changing the temperature on the speed of a reaction. Diagram: Solution A Solution B measuring cylinder + LO: I know how temperature affects the speed of reaction.

37. Method: 1. 25cm3 of solution B was added to 25cm3 of solution A in a beaker. 2. The time taken for the blue/black colour to appear was measured. 3. The temperature was recorded. 4. Steps 1 to 3 were repeated except solution A was heated to 40˚C first. Result: Conclusion: The higher the temperature, the faster the speed of the reaction. LO: I know how temperature affects the speed of a reaction.

38. Examples: faster A car exhaust rusts than the rest of the car. slower Food goes off in the fridge and even in the freezer. slower slower Biological washing powder works in cold water than in warm water. faster Plants grow in a greenhouse than outside. LO: I know how temperature affects the speed of a reaction.

39. (c) Change in Concentration The number of particles in a particular volume of gas or liquid is known as the concentration. Low concentration High concentration (dilute) (concentrated) The concentration of a solution is usually written on the bottle, eg, 1M or 0.1M. LO: I know what is meant by concentration.

40. To show the effect of changing the concentration on the speed of a reaction. Aim: Diagram: carbon dioxide fill line water hydrochloric acid marble chips LO: I know how concentration affects the speed of a reaction.

41. Method: 1. The apparatus was set up as shown. 2. 10cm3 of 0.5M acid was added to 4 pieces of marble. 3. The time taken for the gas to fill to the line was measured. 4. Steps 1 and 2 were repeated using 1M and 1.5M acid. Result: LO: I know how concentration affects the speed of a reaction.

42. Graph: Time (s) Concentration (M) Conclusion: The higher the concentration, the faster the speed of the reaction. LO: I know how concentration affects the speed of a reaction.

43. Examples: faster Ships rust at sea than on a river because of the higher concentration of salt. slower Statues corrode in the country than the city because of the lower concentration of acid rain. faster Plants grow when carbon dioxide is added to the air in the greenhouse. hotter Fires burn when air (oxygen) is blown on them. LO: I know how concentration affects the speed of a reaction.

44. (d) Catalysts Aim: To show the effect of adding a catalyst on the speed of a reaction. Diagram: Before After LO: I know how catalysts affect the speed of a reaction.

45. Method: 1. 25cm3 of solution A was added to 25cm3 of solution B in a beaker. 2. The mixture was heated to 50˚C. 3. 10cm3 of the catalyst was added. Result: The mixture was pink at the beginning, then green with lots of bubbles and back to pink at the end of the reaction. Conclusion: A catalyst speeds up a reaction without being used up itself. LO: I know how temperature affects the speed of a reaction.

46. Examples: exhausts Catalytic convertors in car change harmful gases into less harmful ones. Some washing powders use biological catalysts to remove from clothing. stains LO: I know how catalysts affect the speed of a reaction.

47. Summary The speed of a chemical reaction can be increased by: • the particle size. decreasing increasing • the temperature. • the concentration. increasing • adding a . catalyst LO: I know how to change the speed of a chemical reaction.