1. Unit 5: Chemical Equations and Reactions Chemistry CPA Winter 2014 Callahan, Pengitore & Ricafort

2. Unit Objectives Unit Objectives: To relate chemical changes and macroscopic properties (5 signs of a chemical reaction) To demonstrate how chemical equations describe chemical reactions To illustrate how to balance chemical reactions by changing coefficients To distinguish between the five major types of chemical reactions To classify a reaction as belonging to one of five major types. To classify factors that influence the rate of reaction.

3. Unit 5 Standards: NJCCCS: 5.1.12.A-D, 5.2.12.A.5, 5.2.12.B.2, 5.2.12.B.3, 5.2.12.D.5 CCCS: ELA-Literacy.RST.11-12.3, 4, 5, 7, 8, 9, 10

4. Chemical Equation represents a chemical change or reaction Reactants  Products Reactants – chemicals before the reaction Products – substance formed in the reaction

5. 5 signs of a chemical reaction 1. Color Change

6. 5 signs of a chemical reaction 2. Precipitation of a Solid

7. 5 signs of a chemical reaction 3. Energy Change – heat or light absorbed or released

8. 5 signs of a chemical reaction 4. Odor Changes

9. 5 signs of a chemical reaction 5. Gas Release

10. Reactions can be described several ways: 1. In a sentence Copper reacts with chlorine to form copper (II) chloride. 2. In a word equation Copper + chlorine  copper (II) chloride 3.Using formulas Cu + Cl 2  CuCl 2

11. Symbols used in Reactions SymbolExplanation +Used to separate two reactants or two products  Yields, separates reactants and products (s), (l), (g)State of matter; Fe (s) (aq)Aqueous solution – dissolved in water Heat supplied to the rxn Catalyst used (speeds up the rxn time)

12. Diatomic Elements

13. There are 7 elements on the periodic table that exist in nature bonded in pairs. Those elements are: – Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine, and Iodine. Whenever they are referred to as alone or as a gas, i.e, “chlorine gas”, we write them like this: – H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2

14. Diatomic Elements To help you remember them, you can use the acronym, “HONClBrIF” Or, with the exception of Hydrogen, they make the number “7” on the periodic table starting at Nitrogen, going down to Iodine:

15. Practice Problem Set: Write the word equations below as chemical equations 1. Zinc and lead (II) nitrate react to form zinc nitrate and lead. 2.Aluminum bromide and chlorine gas react to form aluminum chloride and bromine gas. 3.Sodium hydroxide and carbon dioxide react to form sodium carbonate and water (dihydrogen monoxide)

16. In a chemical reaction Law of Conservation of Matter states that matter isn’t created or destroyed. The way atoms are joined is changed

17. Because of the LAW OF CONSERVATION OF MATTER, we have to BALANCE EQUATIONS!!! To BALANCE AN EQUATION means to make sure that the NUMBER of atoms of each element is the same in the reactants and in the products!

18. Balancing Rules: 1.You may change the coefficients to any number you want, but… 2.You may NEVER change a subscript. A coefficient is a number written in front of the compound

19. Balancing example #1 C + O  CO 2

20. Balancing example #2 Zn + HCl  H 2 + ZnCl 2

21. Balancing example #3 CuO + C  Cu+ CO 2

22. Balancing example #4 O 3  O 2

23. Balancing example #5 Al + CuCl 2  Cu + AlCl 3

24. Balancing example #6 C + H 2  C 3 H 8

25. Balancing example #7 CF 4 + Br 2  CBr 4 + F 2

26. Balancing example #8 Hg 2 I 2 + O 2  Hg 2 O + I 2

27. Balancing example #9 N 2 + H 2  NH 3

28. Balancing example #10 KClO 3  KCl + O 2

29. Balancing example #11 H 2 + O 2  H 2 O

30. Balancing example #12 AlBr 3 + K 2 SO 4  KBr + Al 2 (SO 4 ) 3

31. 5 Types of Chemical Reactions 1.Synthesis 2.Decomposition 3.Single Replacement (Displacement) 4.Double Replacement (Displacement) 5.Combustion

32. Synthesis Reaction Synthesis reaction – 2 substances are combined to form a single product A + B  AB + 

33. Synthesis Examples 2Mg + O 2  2MgO Magnesium and oxygen combine to form magnesium oxide. 2H 2 + O 2  2H 2 O Hydrogen and oxygen combine to form dihydrogen monoxide (water)

34. Synthesis Demo Ignite magnesium

35. Decomposition Reaction Decomposition reaction – A single compound is broken down into 2 or more products. AB  A + B  +

36. Decomposition Examples 2NaCl(s)  2Na(s) + Cl 2 (g) Sodium chloride (table salt) decomposes into sodium and chlorine gas. CaCO 3  CaO + CO 2 Limestone (CaCO 3 ) decomposes into lime (CaO) and carbon dioxide.

37. Decomposition Demo Decomposition of Hydrogen Peroxide with MnO 2 as a catalyst H 2 O 2  O 2 + H 2 O

38. Single Replacement Reaction Single Replacement reaction – A single element takes the place of an element in a compound. A + BC  B + AC +  +

39. Single Replacement Examples Mg + BeO  Be + MgO Magnesium replaces beryllium in beryllium oxide to form magnesium oxide and beryllium. 2Na + 2HCl  H 2 + 2NaCl Sodium replaces hydrogen in hydrochloric acid to yield hydrogen and sodium chloride.

40. Single Replacement Demo Magnesium reacting with Hydrochloric acid Compared to Copper reacting with HCl

41. Double Replacement Reaction Double Replacement reaction – Elements in 2 compounds switch places to form 2 new compounds. AB + CD  AD + CB +  +

42. Double Replacement Examples MgO + BeS  MgS + BeO Oxygen and sulfur switch places to form magnesium sulfide and beryllium oxide. Na 2 S + Zn(NO 3 ) 2  2Na(NO 3 ) + ZnS Sulfur and nitrate switch places to form sodium nitrate and zinc sulfide.

43. Double Replacement Demo A double replacement between barium chloride and potassium sulfate Potassium Iodide and lead (II) nitrate produces potassium nitrate and lead (II) iodide

44. Combustion Reaction Combustion reaction – hydrocarbon (H and C) burn in oxygen to produce water and carbon dioxide. Heat is given off as energy. C x H y + O 2  H 2 O + CO 2

45. Combustion Examples CH 4 + 2O 2  2H 2 O + CO 2 Methane burns in oxygen to produce water and carbon dioxide. C 12 H 22 O 11 + 12O 2  11H 2 O + 12CO 2 A sugar molecule burns in oxygen to produce water and carbon dioxide

46. Combustion Demo Burn sugar Burn gasoline

47. Factors that affect reaction rates Temperature – Higher temperature faster reaction Concentration – Changing the amounts of reactants – High concentration means more particles per volume – Example: 3% H 2 O 2 vs. 30% H 2 O 2

48. Surface Area – Reactions occur faster when there is more surface area Sugar cube vs. sugar packet dissolving Catalyst – Used to speed up a reaction without being used up – Enzymes are examples of catalyst

49. Can you slow a reaction down? Inhibitor – a substance added to slow reactions down – Added to food products

50. Limiting Reactant Sometimes, when two or more reactants are present in a reaction, more than the other is available for reacting. The one thing that there is not enough of is called the limiting reactant. It is the reactant that is used up first.

51. Limiting Reactant Example #1: Making a Bicycle Making a bicycle requires 1 frame + 2 wheels  1 bicycle a)If you have 100 frames and 120 wheels, how many bicycles can you manufacture? ______ a)What is the limiting reactant? _________

52. Limiting Reactant Example #2: Grilled Cheese Sandwich Bread + Cheese  ‘Cheese Melt’ 2 B + C  B 2 C 100 bread 30 slices ? sandwiches

53. Limiting Reactant Example #3: Chemistry Problem Hydrogen gas can be produced by the reaction of magnesium and hydrochloric acid, as shown by this equation: Mg(s) + 2HCl (aq)  MgCl 2 (aq) + H 2 (g) In particular, 6,000 molecules of HCl were mixed with 1,000 molecules of Mg. a)Which reactant is limiting? ________________________ a)How many molecules of H 2 are formed when the reaction is complete? ______________________________________