1. Chapter 8 Chemical Reactions by Christopher Hamaker
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Chapter 8

2. Chemical and Physical Changes
In a physical change, the chemical composition of the substance remains constant.
Examples of physical changes are the melting of ice or the boiling of water.
In a chemical change, the chemical composition of the substance changes; a chemical reaction occurs.
During a chemical reaction, a new substance is formed.
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Chapter 8

3. Chemistry Connection: Fireworks
The bright colors seen in a fireworks display are caused by chemical compounds, specifically the metal ions in ionic compounds.
Each metal produces a different color.
Na compounds are orange-yellow.
Ba compounds are yellow-green.
Ca compounds are red-orange.
Sr compounds are bright red.
Li compounds are scarlet red.
Cu compounds are blue-green.
Al or Mg metal produces white sparks.
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Chapter 8

4. Evidence for Chemical Reactions
There are four observations that indicate a chemical reaction is taking place.
A gas is released.
Gas may be observed in many ways in a reaction from light fizzing to heavy bubbling.
The release of hydrogen gas from the reaction of magnesium metal with acid is shown here.
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5. Evidence for Chemical Reactions, Continued
An insoluble solid is produced.
A substance dissolves in water to give an aqueous solution.
If we add two aqueous solutions together, we may observe the production of a solid substance.
The insoluble solid formed is called a precipitate.
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6. Evidence for Chemical Reactions, Continued
A permanent color change is observed.
Many chemical reactions involve a permanent color change.
A change in color indicates that a new substance has been formed.
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Chapter 8

7. Evidence for Chemical Reactions, Continued
A heat energy change is observed.
A reaction that releases heat is an exothermic reaction.
A reaction that absorbs heat is an endothermic reaction.
Examples of a heat energy change in a chemical reaction are heat and light being given off.
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Chapter 8

8. Example Video Evidence of a Chemical Reaction (2:53 min)
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Chapter 4

9. Writing Chemical Equations
A chemical equation describes a chemical reaction using formulas and symbols. A general chemical equation is as follows:
A + B → C + D
In this equation, A and B are reactants and C and D are products.
We can also add a catalyst to a reaction. A catalyst is written above the arrow and speeds up the reaction without being consumed.
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Chapter 8

10. States of Matter in Equations
When writing chemical equations, we usually specify the physical state of the reactants and products.
A(g) + B(l) → C(s) + D(aq)
In this equation, reactant A is in the gaseous state and reactant B is in the liquid state.
Also, product C is in the solid state and product D is in the aqueous state.
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Chapter 8

11. Chemical Reactions: Equations
Writing chemical equations
A chemical equation is the symbolic representation of a chemical reaction in terms of chemical formulas.
For example, the burning of sodium and chlorine to produce sodium chloride is written
The reactants are starting substances in a chemical reaction. The arrow means “yields.” The formulas on the right side of the arrow represent the products. 2

12. Chemical Reactions: Equations
In many cases, it is useful to indicate the states of the substances in the equation.
Writing chemical equations
When you use these labels, the previous equation becomes 2

13. Chemical Equation Symbols
Here are several symbols used in chemical equations:
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14. Features of a Chemical Equation
 - means heat is needed.
Products and reactants must be specified using chemical symbols
Reactants- written on the left of arrow
Products - written on the right
Physical states are shown in parentheses

15. HC2H3O2(aq) + NaHCO3(s) → NaC2H3O2(aq) + H2O(l) + CO2(g)
A Chemical Reaction
Let’s look at a chemical reaction:
HC2H3O2(aq) + NaHCO3(s) → NaC2H3O2(aq) + H2O(l) + CO2(g)
The equation can be read as follows:
Aqueous acetic acid is added to solid sodium carbonate and yields aqueous sodium acetate, liquid water, and carbon dioxide gas.
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Chapter 8

16. Diatomic Molecules
Seven nonmetals occur naturally as diatomic molecules:
Hydrogen (H2)
Nitrogen (N2)
Oxygen (O2)
Halogen F2
Halogen Cl2
Halogen Br2
Halogen I2
These elements are written as diatomic molecules when they appear in chemical reactions.
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Chapter 8

17. Example Video Chemistry - How to Write Chemical Equations (5:11 min)
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Chapter 4

18. Balancing Chemical Equations
When we write a chemical equation, the number of atoms of each element must be the same on both sides of the arrow.
This is called a balanced chemical equation.
We balance chemical reactions by placing a whole number coefficient in front of each substance.
A coefficient multiplies all subscripts in a chemical formula:
3 H2O has 6 hydrogen atoms and 3 oxygen atoms.
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Chapter 8

19. Guidelines for Balancing Equations
Before placing coefficients in an equation, check that the formulas are correct.
Never change the subscripts in a chemical formula to balance a chemical equation.
Balance each element in the equation starting with the most complex formula.
Balance polyatomic ions as a single unit if it appears on both sides of the equation.
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Chapter 8

20. Chemical Reactions: Equations
Writing chemical equations
The law of conservation of mass dictates that the total number of atoms of each element on both sides of a chemical equation must match. The equation is then said to be balanced.
Consider the combustion of methane to produce carbon dioxide and water. 2

21. Chemical Reactions: Equations
Writing chemical equations
For this equation to balance, two molecules of oxygen must be consumed for each molecule of methane, producing one molecule of CO2 and two molecules of water.
Now the equation is “balanced.” 2 2

22. Guidelines for Balancing Equations, Continued
The coefficients must be whole numbers. If you get a fraction, multiply the whole equation by the denominator to get whole numbers.
[H2(g) + ½ O2(g) → H2O(l)] x 2
2 H2(g) + O2(g) → 2 H2O(l)
After balancing the equation, check that there are the same number of atoms of each element (or polyatomic ion) on both sides of the equation.
2(2) = 4 H; 2 O → 2(2) = 4 H; 2 O
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23. Guidelines for Balancing Equations, Continued
Finally, check that you have the smallest whole number ratio of coefficients. If you can divide all the coefficients by a common factor, do so to complete your balancing of the reaction.
[2 H2(g) + 2 Br2(g) → 4 HBr(g)] ÷ 2
H2(g) + Br2(g) → 2 HBr(g)
2 H; 2 Br → 2(1) = 2 H; 2(1) = 2 Br
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Chapter 8

24. Balancing a Chemical Equation
Balance the following chemical equation:
__Al2(SO4)3(aq) + __Ba(NO3)2(aq) → __Al(NO3)3(aq) + __BaSO4(s)
There is one SO4 on the right and three on the left. Place a 3 in front of BaSO4. There are two Al on the left, and one on the right. Place a 2 in front of Al(NO3)3.
Al2(SO4)3(aq) + __Ba(NO3)2(aq) → 2 Al(NO3)3(aq) + 3 BaSO4(s)
There are three Ba on the right and one on the left. Place a 3 in front of Ba(NO3)2.
Al2(SO4)3(aq) + 3 Ba(NO3)2(aq) → 2 Al(NO3)3(aq) + 3 BaSO4(s)
2 Al, 3 SO4, 3 Ba, 6 NO3 → 2 Al, 6 NO3, 3 Ba, 3 SO4
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25. Example Video Balancing Chemical Equations (14:28 min)
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Chapter 4

26. Let's Practice Balancing
Balance the following equations:
1. C2H2 + O2  CO2 + H2O
2. AgNO3 + FeCl3  Fe(NO3)3 + AgCl
3. C2H6 + O2  CO2 + H2O
4. N2 + H2  NH3

27. Classifying Chemical Reactions
We can place chemical reactions into five categories:
Combination (Synthesis) reactions
Decomposition reactions
Single-replacement reactions
Double-replacement reactions
Neutralization reactions
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28. Example Video
Classifying Chemical Reactions Flintstones.wmv (3:08 min)
Neutralization reaction (0:59 min)
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Chapter 4

29. Combination Reactions
A combination reaction is a reaction in which two simpler substances are combined into a more complex compound.
Combination reactions are also called synthesis reactions.
We will look at three combination reactions:
The reaction of a metal with oxygen
The reaction of a nonmetal with oxygen
The reaction of a metal and a nonmetal
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Chapter 8

30. Reactions of Metals with Oxygen
When a metal is heated with oxygen gas, a metal oxide is produced.
metal + oxygen gas → metal oxide
For example, magnesium metal produces magnesium oxide.
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31. Reactions of Nonmetals with Oxygen
Oxygen and a nonmetal react to produce a nonmetal oxide.
nonmetal + oxygen gas → nonmetal oxide
Sulfur reacts with oxygen to produce sulfur dioxide gas.
S(s) + O2(g) → SO2(g)
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Chapter 8

32. Metal + Nonmetal Reactions
A metal and a nonmetal react in a combination reaction to give an ionic compound.
metal + nonmetal → ionic compound
Sodium reacts with chlorine gas to produce sodium chloride.
2 Na(s) + Cl2(g) → 2 NaCl(s)
When a main group metal reacts with a nonmetal, the formula of the ionic compound is predictable. If the compound contains a transition metal, the formula is not predictable.
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33. Example Video Combination Reaction (0:54 min)
Combination Reactions (3:25 min)
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Chapter 4

34. Decomposition Reactions
In a decomposition reaction, a single compound is broken down into simpler substances.
Heat or light is usually required to start a decomposition reaction. Ionic compounds containing oxygen often decompose into a metal and oxygen gas.
For example, heating solid mercury(II) oxide produces mercury metal and oxygen gas.
2 HgO(s) → 2 Hg(l) + O2(g)
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Chapter 8

35. Carbonate Decompositions
Metal hydrogen carbonates decompose to give a metal carbonate, water, and carbon dioxide.
For example, nickel(II) hydrogen carbonate decomposes as follows:
Ni(HCO3)2(s) → NiCO3(s) + H2O(l) + CO2(g)
Metal carbonates decompose to give a metal oxide and carbon dioxide gas.
For example, calcium carbonate decomposes as follows:
CaCO3(s) → CaO(s) + CO2(g)
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36. Example Video Decomposition Reaction (2:42 min)
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Chapter 4

37. Activity Series Concept
When a metal undergoes a replacement reaction, it displaces another metal from a compound or aqueous solution.
The metal that displaces the other metal does so because it is more active.
The activity of a metal is a measure of its ability to compete in a replacement reaction.
In an activity series, a sequence of metals is arranged according to its ability to undergo a reaction.
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Chapter 8

38. Activity Series
Metals that are most reactive appear first in the activity series.
Metals that are least reactive appear last in the activity series.
The relative activity series is:
Li > K > Ba > Sr > Ca > Na > Mg >
Al > Mn > Zn > Fe > Cd > Co > Ni >
Sn > Pb > (H) > Cu > Ag > Hg > Au
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39. Example Video Activity Series (6:29 min)
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Chapter 4

40. Single-Replacement Reactions
A single-replacement reaction is a reaction in which a more active metal displaces another less active metal in a compound.
If a metal precedes another in the activity series, it will undergo a single-replacement reaction.
Fe(s) + CuSO4(aq) →
FeSO4(aq) + Cu(s)
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Chapter 8

41. Aqueous Acid Displacements
Metals that precede (H) in the activity series react with acids, and those that follow (H) do not react with acids.
More active metals react with acid to produce hydrogen gas and an ionic compound.
Fe(s) + 2 HCl(aq) → FeCl2(aq) + H2(g)
Metals less active than (H) show no reaction.
Au(s) + H2SO4(aq) → NR
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Chapter 8

42. Active Metals
A few metals are active enough to react directly with water. These are called active metals.
The active metals are Li, Na, K, Rb, Cs, Ca, Sr, and Ba.
They react with water to produce a metal hydroxide and hydrogen gas.
2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g)
Ca(s) + 2 H2O(l) → Ca(OH)2(aq) + H2(g)
Unnumbered figure, bottom left margin page 218 (magnesium in water)
Custom animate to appear with 3rd line of text
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Chapter 8

43. Example Video Single Replacement Reactions (3:16 min)
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Chapter 4

44. Types of Chemical Reactions
Precipitation Reactions
A precipitation reaction occurs in aqueous solution because one product is insoluble.
A precipitate is an insoluble solid compound formed during a chemical reaction in solution.
For example, the reaction of sodium chloride with silver nitrate forms AgCl(s), an insoluble precipitate.

45. Reaction of magnesium chloride and silver nitrate
Reaction of magnesium chloride and silver nitrate. Photo courtesy of American Color.

47. Precipitation Reactions
Precipitate – insoluble solid that separates from solution
PbI2
precipitate
Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq)
molecular equation
Pb2+ + 2NO3- + 2Na+ + 2I PbI2 (s) + 2Na+ + 2NO3-
ionic equation
Pb2+ + 2I PbI2 (s)
net ionic equation
Na+ and NO3- are spectator ions

48. Precipitation of Lead Iodide
Pb2+ + 2I PbI2 (s)
PbI2

49. Types of Chemical Reactions
Solubility rules
Precipitation Reactions
Substances vary widely in their solubility, or ability to dissolve, in water.
For example, NaCl is very soluble in water whereas calcium carbonate, CaCO3, is insoluble in water.

50. Types of Chemical Reactions
Predicting Precipitation Reactions.
Precipitation Reactions
To predict whether a precipitate will form, we need to look at potential insoluble products.
Next slide - Table lists eight solubility rules for ionic compounds. These rules apply to the most common ionic compounds.

51. Solubility Rules
Not all ionic compounds are soluble in water. We can use the solubility rules to predict if a compound will be soluble in water.
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Chapter 8

52. Double-Replacement Reactions
In a double-replacement reaction, two ionic compounds in aqueous solution switch anions and produce two new compounds.
AX + BZ → AZ + BX
If either AZ or BX is an insoluble compound, a precipitate will appear and there is a chemical reaction.
If no precipitate is formed, there is no reaction.
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53. Double-Replacement Reactions, Continued
Aqueous barium chloride reacts with aqueous potassium chromate as follows:
2 BaCl2(aq) + K2CrO4(aq) → BaCrO4(s) + 2 KCl(aq)
From the solubility rules, BaCrO4 is insoluble, so there is a double-replacement reaction.
Aqueous sodium chloride reacts with aqueous lithium nitrate as follows:
NaCl(aq) + LiNO3(aq) → NaNO3(aq) + LiCl(aq)
Both NaNO3 and LiCl are soluble, so there is no reaction.
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Chapter 8

54. Types of Chemical Reactions
Predicting Precipitation Reactions.
Precipitation Reactions
Suppose you mix together solutions of nickel(II) chloride, NiCl2, and sodium phosphate, Na3PO4.
How can you tell if a reaction will occur, and if it does, what products to expect?

55. Types of Chemical Reactions
Predicting Precipitation Reactions.
Precipitation Reactions
Precipitation reactions have the form of an “exchange reaction.”
An exchange (or metathesis) reaction is a reaction between compounds that, when written as a molecular equation, appears to involve an exchange of cations and anions.

56. Types of Chemical Reactions
Precipitation Reactions
Predicting Precipitation Reactions.
Now that we have predicted potential products, we must balance the equation.
We must verify that NiCl2 and Na3PO4 are soluble and then check the solubilities of the products.

57. Types of Chemical Reactions
Predicting Precipitation Reactions.
Precipitation Reactions
The solubility table indicates that our reactants, nickel(II) chloride and sodium phosphate are both soluble.
(aq) (aq)
(s) (aq)
Looking at the potential products we find that nickel(II) phosphate is not soluble although sodium chloride is.

58. Types of Chemical Reactions
Predicting Precipitation Reactions.
Precipitation Reactions
We predict that a reaction occurs because nickel(II) phosphate is insoluble and precipitates from the reaction mixture.
To see the reaction that occurs on the ionic level, we must rewrite the molecular equation as an ionic equation.

59. Types of Chemical Reactions
Predicting Precipitation Reactions.
Precipitation Reactions
First write strong electrolytes (the soluble ionic compounds) in the form of ions to obtain the complete ionic equation

60. Types of Chemical Reactions
Precipitation Reactions
Predicting Precipitation Reactions.
After canceling the spectator ions, you obtain the net ionic equation.
This equation represents the “essential” reaction.

61. Example Video
reaction of LEAD NITRATE & POTASSIUM IODIDE solutions (1:48 min)
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Chapter 4

62. Neutralization Reactions
A neutralization reaction is the reaction of an acid and a base.
HX + BOH → BX + HOH
A neutralization reaction produces a salt and water.
H2SO4(aq) + 2 KOH(aq) → K2SO4(aq) + 2 H2O(l)
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Chapter 8

63. Acids Have a sour taste. Vinegar owes its taste to acetic acid. Citrus
fruits contain citric acid.
React with certain metals to produce hydrogen gas.
2HCl (aq) + Mg (s) MgCl2 (aq) + H2 (g)
React with carbonates and bicarbonates to produce carbon
dioxide gas
2HCl (aq) + CaCO3 (s) CaCl2 (aq) + CO2 (g) + H2O (l)
Aqueous acid solutions conduct electricity.

64. Bases Have a bitter taste. Feel slippery. Many soaps contain bases.
Cause color changes in plant dyes.
Aqueous base solutions conduct electricity.

65. Pg 129

67. Common Household acids and bases.

68. Neutralization Reaction
acid + base salt + water
HCl (aq) + NaOH (aq) NaCl (aq) + H2O
H+ + Cl- + Na+ + OH Na+ + Cl- + H2O
H+ + OH H2O

69. Types of Chemical Reactions
Acid-Base Reactions
Neutralization Reactions
One of the chemical properties of acids and bases is that they neutralize one another.
A neutralization reaction is a reaction of an acid and a base that results in an ionic compound and water.
The ionic compound that is the product of a neutralization reaction is called a salt.
acid
base
salt

70. Types of Chemical Reactions
Acid-Base Reactions
Neutralization Reactions
The net ionic equation for each acid-base neutralization reaction involves a transfer of a proton.
Consider the reaction of the strong acid , HCl(aq) and a strong base, LiOH(aq).

71. Types of Chemical Reactions
Acid-Base Reactions
Neutralization Reactions
Writing the strong electrolytes in the form of ions gives the following complete ionic equation.

72. Types of Chemical Reactions
Acid-Base Reactions
Neutralization Reactions
Canceling the spectator ions results in the net ionic equation. Note the proton transfer. H+

73. Types of Chemical Reactions
Acid-Base Reactions
Neutralization Reactions
In a reaction involving HCN(aq), a weak acid, and KOH(aq), a strong base, the product is KCN, a strong electrolyte
Referring to Tables 4.1, 4.2 and 4.3, we obtain this net ionic equation: H+
Note the proton transfer.

74. Chapter Summary
There are four ways to tell if a chemical reaction has occurred:
A gas is detected.
A precipitate is formed.
A permanent color change is seen.
Heat or light is given off.
An exothermic reaction gives off heat and an endothermic reaction absorbs heat.
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75. Chapter Summary, Continued
There are seven elements that exist as diatomic molecules: H2 N2 O2 F2
Cl2
Br2 I2
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76. Chapter Summary, Continued
When we balance a chemical equation, the number of each type of atom must be the same on both the product and reactant sides of the equation.
We use coefficients in front of compounds to balance chemical reactions.
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77. Chapter Summary, Continued
There are five basic types of chemical reactions.
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78. Chapter Summary, Continued
In combination reactions, two or more smaller molecules are combined into a more complex molecule.
In a decomposition reaction, a molecule breaks apart into two or more simpler molecules.
In a single-replacement reaction, a more active metal displaces a less active metal according to the activity series.
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Chapter 8

79. Chapter Summary, Continued
In a double-replacement reaction, two aqueous solutions produce a precipitate of an insoluble compound.
The insoluble compound can be predicted based on the solubility rules.
In a neutralization reaction, an acid and a base react to produce a salt and water.
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Chapter 8