1. Chapter 8 Table of Contents Section 1 Describing Chemical Reactions
Chemical Equations and Reactions
Chapter 8
Table of Contents
Section 1 Describing Chemical Reactions
Section 2 Balancing Chemical Equations
Section 3 Classifying Chemical Reactions
Section 4 Writing Net Ionic Equations

2. Section 1 Describing Chemical Reactions
Chapter 8
Bellringer
For the following situations, list observations that you think indicate that a chemical reaction has taken place:
a cut apple turns brown
an egg changes when it cooks
a log burns
a car rusts

3. Chapter 8 Objectives (Slides 2-15)
Section 1 Describing Chemical Reactions
Chapter 8
Objectives (Slides 2-15)
List evidence that suggests that a chemical reaction has occurred and evidence that proves that a chemical reaction has occurred.
Describe a chemical reaction by using a word equation and a formula equation.
Interpret notations in formula equations, such as those relating to states of matter or reaction conditions.

4. Chapter 8 Chemical Reaction
Section 1 Describing Chemical Reactions
Chapter 8
Chemical Reaction
A chemical reaction is the process by which one or more substances change into one or more new substances.
Reactants are the original substances in a chemical reaction.
Products are the substances that are created in a chemical reaction.

5. Evidence of a Chemical Reaction
Section 1 Describing Chemical Reactions
Chapter 8
Evidence of a Chemical Reaction

6. Signs of a Chemical Reaction
Chapter 8
Visual Concepts
Signs of a Chemical Reaction

7. Chapter 8
Visual Concepts
Precipitate

8. Evidence of a Chemical Reaction
Section 1 Describing Chemical Reactions
Chapter 8
Evidence of a Chemical Reaction
solution color changes
solution bubbles
copper is used up

9. Chemical Reaction Versus Physical Change
Section 1 Describing Chemical Reactions
Chapter 8
Chemical Reaction Versus Physical Change
chemical change – new substance forms with properties that differ from original substance
density
boiling point
melting point
physical change - changes of state
evaporation
condensation
melting
freezing

10. Reactions and Energy Changes
Section 1 Describing Chemical Reactions
Chapter 8
Reactions and Energy Changes
Energy can be released in a chemical reaction.
methane + oxygen  carbon dioxide + water + energy
Energy is a product.
Energy can be absorbed in a chemical reaction.
dinitrogen tetroxide + energy  nitrogen dioxide
Energy is a reactant.

11. Constructing a Chemical Equation
Section 1 Describing Chemical Reactions
Chapter 8
Constructing a Chemical Equation
A chemical equation shows the chemical formulas and relative amounts of all reactants and products.
A word equation contains the names of the reactants and products.
Equations must be balanced.

12. methane + oxygen  carbon dioxide + water
Section 1 Describing Chemical Reactions
Chapter 8
Writing a Word Equation or Formula Equation
methane + oxygen  carbon dioxide + water
?CH ?O2  ?CO ?H2O

13. Equations and Reaction Information
Section 1 Describing Chemical Reactions
Chapter 8
Equations and Reaction Information
Physical States
NaHCO3(s) + HC2H3O2(aq)  NaC2H3O2(aq) + CO2(aq) + H2O(l)
solid liquid
aqueous solutions
Reaction Conditions
350°C, kPa
N2(g) + 3H2(g)
2NH3(g)
catalyst

14. Equations and Reaction Information
Section 1 Describing Chemical Reactions
Chapter 8
Equations and Reaction Information

15. Chapter 8
Visual Concepts
Chemical Equation

16. sugar + flour + eggs + vanilla + salt  cake
Section 2 Balancing Chemical Equations
Chapter 8
Bellringer
Write a word equation for baking a cake.
Does the cake have the same properties as the ingredients?
Answer:
sugar + flour + eggs + vanilla + salt  cake
The properties are different.

17. Chapter 8 Objectives (slides 16- 27)
Section 2 Balancing Chemical Equations
Chapter 8
Objectives (slides )
Relate the conservation of mass to the rearrangement of atoms in a chemical reaction.
Write and interpret a balanced chemical equation for a reaction, and relate conservation of mass to the balanced equation.

18. Reactions Conserve Mass
Section 2 Balancing Chemical Equations
Chapter 8
Reactions Conserve Mass
Mass cannot be created or destroyed by a chemical or physical change
Equations must be balanced.
?Na + ?H2O  ?NaOH + ?H2

19. Chapter 8 Balancing Equations
Section 2 Balancing Chemical Equations
Chapter 8
Balancing Equations
The number of atoms for each element must be the same on the reactants’ side and on the products’ side.
A coefficient multiplies the number of atoms of each element in the formula that follows.
H2O: 2 hydrogen atoms, 1 oxygen atom
2H2O: 4 hydrogen atoms, 2 oxygen atoms

20. Reading a Chemical Equation
Chapter 8
Visual Concepts
Reading a Chemical Equation

21. Chapter 8 Balancing Equations Sample Problem A
Section 2 Balancing Chemical Equations
Chapter 8
Balancing Equations
Sample Problem A
Balance the equation for the reaction of iron(III) oxide with hydrogen to form iron and water.

22. Chapter 8 Balancing Equations Sample Problem A Solution
Section 2 Balancing Chemical Equations
Chapter 8
Balancing Equations
Sample Problem A Solution
Identify reactants and products.
reactants products
Fe2O H2  Fe + H2O
Count atoms 3 2 3
Reactants
Products
Balanced?
Unbalanced formula equation
Fe2O3 + H2
Fe + H2O
Iron atoms 2 1 no
Oxygen atoms 3
Hydrogen atoms
yes
Insert coefficients.

23. Reactions Conserve Mass
Section 2 Balancing Chemical Equations
Chapter 8
Reactions Conserve Mass
Balanced equations show mass conservation
?Na + ?H2O  ?NaOH + ?H2
2Na + 2H2O  2NaOH + H2
Never change subscripts to balance equations
Unbalanced: H2 + O2  H2O
Incorrect: H2 + O2  H2O2
H2O  H2O2
Correct: 2H2 + O2  2H2O

24. Reactions Conserve Mass
Section 2 Balancing Chemical Equations
Chapter 8
Reactions Conserve Mass

25. Polyatomic Ions can be balanced as a group
Section 2 Balancing Chemical Equations
Chapter 8
Polyatomic Ions can be balanced as a group

26. Chapter 8 Balancing Equations
Section 2 Balancing Chemical Equations
Chapter 8
Balancing Equations
Sample Problem C
Aluminum reacts with arsenic acid, HAsO3, to form H2 and aluminum arsenate. Write a balanced equation for this reaction.

27. Chapter 8 Balancing Equations reactants products 2 6 3 2
Section 2 Balancing Chemical Equations
Chapter 8
Balancing Equations
Sample Problem C Solution
1. Identify reactants and products.
reactants products
Al + HAsO3  H Al(AsO3)3
2. Count Atoms 2 6 3 2
Reactants
Products
Balanced?
Unbalanced formula equation
Al + HAsO3
H2 + Al(AsO3)3
Iron atoms 1
yes
Oxygen atoms 2 no
Hydrogen atoms 3
3. Insert coefficients

28. Chapter 8 Bellringer Describe the following terms. synthesis
Section 3 Classifying Chemical Reactions
Chapter 8
Bellringer
Describe the following terms.
synthesis
decomposition
displacement

29. Chapter 8 Objectives (slides 28-49)
Section 3 Classifying Chemical Reactions
Chapter 8
Objectives (slides 28-49)
Identify combustion reactions, and write chemical equations that predict the products.
Identify synthesis reactions, and write chemical equations that predict the products.
Identify decomposition reactions, and write chemical equations that predict the products.

30. Chapter 8 Objectives, continued
Section 3 Classifying Chemical Reactions
Chapter 8
Objectives, continued
Identify displacement reactions, and use the activity series to write chemical equations that predict the products.
Identify double-displacement reactions, and write chemical equations that predict the products.

31. Chapter 8 Combustion Reactions
Section 3 Classifying Chemical Reactions
Chapter 8
Combustion Reactions
A combustion reaction is a reaction of a carbon-based compound with oxygen.
Combustion of propane:
C3H8 + 5O2  3CO2 + 4H2O
Combustion of ethanol:
CH3CH2OH + 3O2  2CO2 + 3H2O

32. Chapter 8
Visual Concepts
Combustion Reaction

33. CaO(s) + H2O(l)  Ca(OH)2(s)
Section 3 Classifying Chemical Reactions
Chapter 8
Synthesis Reactions
In a synthesis reaction a single compound forms from two or more reactants.
Two elements form a binary compound
C + O2  CO2
2C + O2 2CO
Two compounds form a ternary compound
CaO(s) + H2O(l)  Ca(OH)2(s)
CO2(g) + H2O(l)  H2CO3(aq)

34. Chapter 8
Visual Concepts
Synthesis Reactions

35. Decomposition Reactions
Section 3 Classifying Chemical Reactions
Chapter 8
Decomposition Reactions
In a decomposition reaction a single compound breaks down, often with the input of energy, into two or more elements or simpler compounds.
Decomposition of water
electricity
2H2O(l)
O2(g) + 2H2(g)
A metal carbonate decomposes to form a metal oxide and carbon dioxide.
heat
CaCO3(s)
CaO(s) + CO2(g)

36. Decomposition Reaction
Chapter 8
Visual Concepts
Decomposition Reaction

37. Chapter 8
Visual Concepts
Electrolysis

38. Decomposition Reactions, continued
Section 3 Classifying Chemical Reactions
Chapter 8
Decomposition Reactions, continued
Sample Problem D
Predicting Products
Predict the product(s) and write a balanced equation for the reaction of potassium with chlorine.

39. Decomposition Reactions, continued
Section 3 Classifying Chemical Reactions
Chapter 8
Decomposition Reactions, continued
Sample Problem D Solution
Reaction is most likely a synthesis reaction, so the product will be binary
Potassium will lose one electron to become a 1+ ion.
Chlorine will gain one electron to become a 1– ion.
K + Cl2  KCl
Balance the equation.
2K + Cl2  2KCl

40. Displacement Reactions
Section 3 Classifying Chemical Reactions
Chapter 8
Displacement Reactions
In a displacement reaction a single element reacts with a compound and displaces another element from the compound.
2Al(s) + 3CuCl2(aq)  2AlCl3(aq) + 3Cu(s)
Aluminum displaces copper.

41. Single Displacement Reaction
Chapter 8
Visual Concepts
Single Displacement Reaction

42. Displacement Reactions, continued
Section 3 Classifying Chemical Reactions
Chapter 8
Displacement Reactions, continued
The activity series ranks the reactivity of elements

43. Chapter 8
Visual Concepts
Activity Series

44. Displacement Reactions, continued
Section 3 Classifying Chemical Reactions
Chapter 8
Displacement Reactions, continued
Sample Problem E
Determining Products by Using the Activity Series Magnesium is added to a solution of lead(II) nitrate. Will a reaction happen? If so, write the equation and balance it.

45. Displacement Reactions, continued
Section 3 Classifying Chemical Reactions
Chapter 8
Displacement Reactions, continued
Sample Problem E Solution
Identify the reactants.
Magnesium will attempt to displace lead from lead(II) nitrate.
Check the activity series.
Magnesium is more active than lead and displaces it.
Write the balanced equation.
Mg + Pb(NO3)2  Pb + Mg(NO3)2

46. HCl(aq) + NaOH(aq)  HOH(l) + NaCl(aq)
Section 3 Classifying Chemical Reactions
Chapter 8
Double-Displacement Reactions
In a double-displacement reaction two compounds in aqueous solution appear to exchange ions and form two new compounds.
One of the products must be a solid precipitate, a gas, or a molecular compound, such as water.
HCl(aq) + NaOH(aq)  HOH(l) + NaCl(aq)

47. Double-Displacement Reaction
Chapter 8
Visual Concepts
Double-Displacement Reaction

48. Chapter 8
Identifying Reactions and Predicting Products

49. Understanding Concepts
Chapter 8
Standardized Test Preparation
Understanding Concepts
2. Which of these sentences correctly states the law of conservation of mass?
F. In a chemical reaction, the mass of the products cannot exceed the mass of the reactants.
G. In a chemical reaction, the mass of the products is always equal to the mass of the reactants.
H. In a chemical reaction, the mass of the products is always less than the mass of the reactants.
I. In a chemical reaction, the mass of the products is always greater than the mass of the reactants.

50. Section 4 Writing Net Ionic Equations
Chapter 8
Bellringer
Write a definition for the word spectator in terms of the part spectators play in a sporting event.

51. Objectives (skip Section 8.4)
Section 4 Writing Net Ionic Equations
Chapter 8
Objectives (skip Section 8.4)
Write total ionic equations for reactions in aqueous solutions.
Identify spectator ions and write net ionic equations for reactions in aqueous solutions.

52. Ionic Equations, continued
Section 4 Writing Net Ionic Equations
Chapter 8
Ionic Equations, continued
Ionic compounds dissolve in water
KI(aq) = K+(aq) + I–(aq)
Pb(NO3)2(aq) = Pb2+(aq) (aq)
Reaction between KI and Pb(NO3)2
2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq)
Total Ionic Equation
2K+(aq) + 2I–(aq) + Pb2+(aq) (aq)
 PbI2(s) + 2K+(aq) (aq)

53. 2I–(aq) + Pb2+(aq)  PbI2(s)
Section 4 Writing Net Ionic Equations
Chapter 8
Ionic Equations, continued
Spectator ions remain unchanged in the solution as aqueous ions. They do not react.
2K+(aq) + 2I–(aq) + Pb2+(aq) (aq)
 PbI2(s) + 2K+(aq) (aq)
The net ionic equation is the chemical equation that shows only the net change.
2I–(aq) + Pb2+(aq)  PbI2(s)

54. Chapter 8
Visual Concepts
Net Ionic Equation

55. Zn(s) + Cu2+(aq)  Cu(s) + Zn2+(aq)
Section 4 Writing Net Ionic Equations
Chapter 8
Ionic Equations, continued
Net Ionic equations can be used for displacement reactions.
Zn(s) + Cu2+(aq) (aq)  Cu(s) + Zn2+(aq) (aq)
net ionic equation
Zn(s) + Cu2+(aq)  Cu(s) + Zn2+(aq)

56. Ionic Equations, continued
Section 4 Writing Net Ionic Equations
Chapter 8
Ionic Equations, continued
Check atoms and charge to balance net ionic equations.
(aq) + Ba2+(aq)  BaSO4(s)
Charge: (2–) + (2+) =
Zn(s) + Cu2+(aq)  Cu(s) + Zn2+(aq)
Charge:

57. Chapter 8
Writing a Net Ionic Equation