UNIT 2. Chemical Reactions. Chapter 4: Developing Chemical Equations. Chapter 5:Classifying. Chemical Reactions. Chapter 6:Acids and Bases

Transcription

1 UNIT 2 Chemical Reactions Chapter 4: Developing Chemical Equations Chapter 5:Classifying Chemical Reactions Chapter 6:Acids and Bases

2 CHAPTER 5 Classifying Chemical Reactions In this chapter, you will: describe evidence of chemical reactions identify reactants and products of the four reaction types discuss chemical reactions associated with environmental concerns

3 Introductory Activity 5.1 : Foiled Again! With a reaction such as the one shown on page 177, answer the following questions. (Page 177) What changes do you observe? Why is this a chemical change? What were the reactants and products? What happens to the mass of reactants and products during the reaction?

4 5.1 Synthesis and Decomposition Reactions Metal corrosion led to the damage shown in the picture below. The chemical reaction that occurred is illustrated by the following balanced chemical equation. 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) (Page 179)

5 Evidence of Chemical Change (Page 180) The following images illustrate some examples of evidence that a chemical change has occurred. Gas formation - usually observed as bubbles Precipitate formation an insoluble solid formed during a reaction Colour change a new colour being produced Energy production the production of light or heat by a reaction Difficult to Reverse reaction cannot occur in the opposite direction

6 Synthesis Reactions (Pages ) A synthesis reaction is a chemical reaction in which two or more reactants combine to produce a new product. Examples of synthesis reactions The Haber process to produce ammonia N 2 (g) + 3H 2 (g) 2NH 3 (g) The shuttle blast off 2H 2 (l) + O 2 (l) 2H 2 O(g) The production of smog N 2 (g) + O 2 (g) 2NO 2 (g) and 2NO(g) + O 2 (g) 2NO 2 (g)

7 Precipitation Reactions

8 Precipitation Reactions (Page 180) Click the Start buttons to review your understanding of synthesis reactions that produce precipitate.

9 Synthesis Reactions (Page 181) Review your understanding of synthesis reactions.

10 Decomposition Reactions (Pages ) A decomposition reaction is a chemical reaction in which a compound breaks down (decomposes) into two or more simpler compounds or elements. Examples of decomposition reactions The electrolysis of water 2H 2 O(l) 2H 2 (g) + O 2 (g) A TNT Explosion 2C 7 H 5 N 3 O 6 (s) Decomposition of sodium azide 2NaN 3 (s) 3N 2 (g) + 2Na(s) 3N 2 (g) + 5H 2 O(g) + 7CO(g) + 7C(s)

11 Decomposition Reactions (Pages ) Review your understanding of decomposition reactions.

12 Section 5.1 Review (Page 189) Concepts to be reviewed: evidence of a chemical change synthesis reactions (chemical equation and examples) decomposition reactions (chemical equation and examples)

13 5.2 Displacement Reactions (Page 190) Many industrial processes, such as the one used to isolate nickel from the deposits found around Sudbury, rely on a series of chemical reactions that include the displacement of one element by another to form a new compound.

14 Single Displacement Reactions (Page 191) A single displacement reaction is a chemical reaction in which one element (a reactive metal or nonmetal) takes the place of an element in a compound to produce another element and another compound. A + BC AC + B Where A is a metal A + BC BA + C Where A is a non-metal Examples of single displacement reactions Producing zinc chloride (ZnCl 2 ) and hydrogen gas (H 2 ) Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) Producing copper (Cu) metal Mg(s) + CuSO 4 (aq) MgSO 4 (aq) + Cu (s) Displacing silver (Ag) from silver nitrate (AgNO 3 ) Cu(s) + 2AgNO 3 (aq) Cu(NO 3 ) 2 (aq) + 2Ag(s)

15 Activity Series (Page 192) The activity series is a list of elements organized according to their chemical reactivity. The most reactive element appears on the top, and the least reactive appears at the bottom. Remember! Metals can only replace other metals in a reaction, and nonmetals can only replace other non-metals. Metals higher up on the activity series list will replace metals lower on the list during a single displacement reaction.

16 Single Displacement Reactions (Pages ) Review your understanding of single displacement reactions.

17 Double Displacement Reactions (Pages ) A double displacement reaction is a chemical reaction in which the positive ions of two different compounds exchange places, resulting in the formation of two new compounds one of which may be a precipitate. Producing silver chromate (AgCrO 4 (s) ) (the red precipitate) and potassium nitrate (2KNO 3 (aq))

18 Double Displacement Reactions (Pages ) Review your understanding of double displacement reactions.

19 Chemical Reactions and Food Preservation (Page 197) Sulfur dioxide (SO 2 ) is used to preserve the colour of dried fruit. A double displacement reaction followed by a decomposition reaction releases the sulfur dioxide gas required for the process. The double replacement reaction Na 2 SO 3 (aq) + 2HCl(aq) 2NaCl (aq) + H 2 SO 3 (aq) The decomposition reaction H 2 SO 3 (aq) H 2 O(l) + SO 2 (g)

20 Summary of Reaction Types (Page 197)

21 Summary of Reaction Types (Page 197) One additional type of chemical reaction that you will learn about in future studies is a combustion reaction. These reactions always involve a fuel reacting with oxygen to release energy. Carbon dioxide and water are also produced by the reaction.

22 Section 5.2 Review (Page 198) Concepts to be reviewed: single displacement reactions the activity series of elements double displacement reactions

23 5.3 Reactions and Environmental Issues (Page 199) Although chemical reactions can cause environmental issues, they can also be used to help solve environmental challenges.

24 Treating Car Exhaust (Pages ) The complete combustion of gasoline in a car s engine is represented by the following chemical equation. 2C 8 H 18 (l) + 25O 2 (g) 16CO 2 (g) + 18H 2 O(g) Incomplete combustion can result in carbon (C) (soot), carbon monoxide (CO), and nitrogen oxides (NO 2 and NO 3 ) entering the air. A catalytic converter installed in a vehicle s exhaust system can help reduce the amounts of these pollutants in the atmosphere.

25 Incomplete Combustion Occurs when there is a lack of oxygen to properly burn the fuel Fuel + oxygen carbon dioxide + water + soot + nitrogen oxides + carbon monoxide (toxic) In Ontario, cars are required to undergo an emission test (combustion analysis) every 2 years to ensure the vehicle is combusting efficiently

26 Recovering Gold using Cyanide and Zinc (Pages ) Cyanide ions (CN - ) are used to extract gold from rock or ore. 4Au(s) + 8NaCN(aq) + O 2 (g) + 2H 2 O (l) 4Na[Au(CN) 2 ](aq) + 4NaOH(aq) Leaching, a technique that removes gold by dissolving it in an aqueous solution, is used to drain the gold away from the ore. Zinc (Zn) can then be used in a single displacement reaction to displace the gold from the solution. 2Na[Au(CN) 2 ](aq) + Zn(s) 2NaCN(aq) + Zn(CN) 2 (aq) + 2Au(s)

27 Cleaning and Disinfecting Pools (Page 203) A variety of compounds containing chlorine (Cl) are used to prevent the growth of bacteria and other organisms in the water in swimming pools and hot tubs. Care must be taken when using these chemicals to ensure that they are effective in disinfecting the water but remain safe for the users.

28 Hazards in the Home (Pages ) Precautions must be taken when using household chemicals. When mixed, reactions could occur that might be detrimental to the user s health.

29 Bleach and Ammonia A Toxic Combination (Page 205) The mixing of bleach (NaClO) (a compound containing chlorine), and ammonia (NH 3 ) can have dire consequences. 2NH 3 (aq) + 2NaClO(aq) 2NaONH 3 (aq) + Cl 2 (g) Toxic chlorine gas (Cl 2 ) is produced in this reaction. Two other ammonia and bleach reactions produce toxic compounds called chloramines (NCl 3 (g) and NH 2 Cl(g)). NH 3 (aq) + 3NaClO(aq) NH 3 (aq) + NaClO(aq) 3NaOH(aq) + NCl 3 (g) NaOH(aq) + NH 2 Cl(g) + =

30 Chemical Safety (Page 204) Be familiar with the WHMIS and HHPS symbols that identify the hazards associated with the handling and use of chemicals at home and in the workplace. Workplace Hazardous Materials Information System (WHMIS)

31 Chemical Safety Hazardous Household Product Symbols (HHPS)

32 Section 5.3 Review (Page 206) Concepts to be reviewed: the use of catalytic converters to help combat exhaust pollutants the chemical reactions involved in gold extraction the hazards involved in the use and handling of household chemicals safe practices for the handling and use of chemicals familiarity with WHMIS and HPPS symbols and warnings