1. Chemical Reactions

2. Chemical Reactions All chemical reactions have two parts:
A substance that undergoes a reaction is called a reactant.
In other words, reactants are the substances you start with.

3. Chemical Reactions
When reactants undergo a chemical change, each new substance formed is called a product.
In other words, the products are the substances you end up with.

4. Chemical Reactions The reactants turn into the products.
Reactants ® Products

5. Chemical Reactions
In a chemical reaction, the way atoms are joined is changed.
Atoms aren’t created or destroyed.

6. Chemical Reactions Chemical reactions can be described several ways.
In a sentence
Copper reacts with chlorine to form copper (II) chloride.
In a word equation
Copper + chlorine ® copper (II) chloride

7. Symbols Used in Equations
The arrow separates the reactants from the products
The arrow reads “reacts to form.”
The plus sign reads “and”

8. Symbols Used in Equations
(s) after the formula - solid
(g) after the formula - gas
(l) after the formula – liquid
(aq) after the formula – aqueous (a solid dissolved in water)

9. Symbols Used in Equations
­ used after a product indicates a gas, same as (g)
¯ used after a product indicates a solid, same as (s)

10. Symbols Used in Equations
indicates a reversible reaction. (More info later)
shows that heat is supplied to the reaction
is used to indicate a catalyst used supplied, in this case, platinum.

11. What is a Catalyst?
A catalyst is a substance that speeds up a reaction without being changed by the reaction.
Enzymes are biological or protein catalysts.

12. Diatomic Elements There are 8 elements that never want to be alone.
They form diatomic molecules.
H2 , N2 , O2 , F2 , Cl2 , Br2 and I2
1 + 7 pattern on the periodic table

13. Diatomic Elements

14. Indications of a Chemical Reaction
The following is an indication that a chemical reaction has occurred:
formation of a precipitate

15. Indications of a Chemical Reaction
The following is an indication that a chemical reaction has occurred:
evolution of a gas

16. Indications of a Chemical Reaction
The following is an indication that a chemical reaction has occurred:
color change

17. Indications of a Chemical Reaction
The following is an indication that a chemical reaction has occurred:
absorption or release of heat

18. Skeleton Equation
A skeleton formula uses formulas and symbols to describe a reaction.
All chemical equations are sentences that describe reactions.

19. Problem Fe2S3 (s) + HCl (g)  FeCl2 (s) + H2S (g)
1) Convert the following sentence to a chemical equation.
a) Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form solid iron (II) chloride and hydrogen sulfide gas.
Fe2S3 (s) + HCl (g)  FeCl2 (s) + H2S (g)

20. Problem HNO3 (aq) + Na2CO3 (s)  H2O (l) + CO2 (g) + NaNO3 (aq)
Convert the following sentence to a chemical equation.
b) Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.
HNO3 (aq) + Na2CO3 (s)  H2O (l) + CO2 (g) + NaNO3 (aq)

21. Problem 2) Convert the following chemical equation to a sentence.
a) Fe (s) + O2 (g) ® Fe2O3 (s)
Solid iron reacts with oxygen gas to form solid iron (III) oxide.

22. Problem Convert the following chemical equation to a sentence.
b) Cu (s) + AgNO3 (aq) ® Ag (s) + Cu(NO3)2 (aq)
Solid copper reacts with silver nitrate dissolved in water to form solid silver and copper (II) nitrate dissolved in water.

23. Balancing Chemical Equations

24. The Balanced Equation Atoms can’t be created or destroyed.
All the atoms we start with we must end up with.
A balanced equation has the same number of each element on both sides of the equation.

25. ® O + C C O O C + O2 ® CO This equation is NOT balanced.
There is one carbon atom on the left and one on the right.
There are two oxygen atoms on the left and only one on the right.

26. O + C C O O
C + O2 ® CO
We need one more oxygen atom in the products.
We can’t change the formula, because it describes what it is.

27. C O O + C O C O
In order to have two oxygen atoms, another CO must be produced.
But where did the other carbon come from?

28. C C O O + O C C O
We must have started with two carbon atoms.

29. C C O O + O C C O
The balanced chemical equation is
2 C + O2 ® 2 CO

30. Rules for Balancing
Write the correct formulas for all the reactants and products.
Count the number of atoms of each type appearing on both sides.
Balance the elements one at a time by adding coefficients (the numbers in front).
Check to make sure it is balanced.

31. Never Never change a subscript to balance an equation.
If you change the formula you are describing a different reaction.

32. Never Never put a coefficient in the middle of a formula.
2 NaCl is okay; Na2Cl is not.

33. H2 + O2 ® H2O Example Make a table to keep track of where you
are in the balancing process.

34. Example ® H2 + O2 H2O Reactants Products 2 H 2 2 O 1
We need twice as much O in the product.

35. Example
H2 + O2 2
H2O
We need 2 oxygen atoms on the product side, so a coefficient of 2 should be placed in front of water.

36. Example
H2 + O2 2
H2O
We must recalculate the number of hydrogen and oxygen atoms on the right. Coefficients are used as multipliers. R P 2 H 2 4 2 O 1 2

37. Example
H2 + O2 2
H2O
Now we need 4 hydrogen atoms on the reactant side. R P 2 H 4 2 O 2

38. Example 2
H2 + O2 2
H2O
A coefficient of 2 should be placed in front of hydrogen gas. R P 4 2 H 4 2 O 2

39. Example 2
H2 + O2 2
H2O
The equation is balanced; it has the same
number of each kind of atom on both sides! R P 4 H 4 2 O 2

40. Example R P 4 2 H 2 4 2 O 1 2 2 H2 + O2 ® 2 H2O This is the answer,
not this.

41. Balancing Hints 1) metals 2) nonmetals 3) hydrogen 4) oxygen
Balance elements in the following order:
1) metals
2) nonmetals
3) hydrogen
4) oxygen

42. Balancing Hints
If an atom appears more than once on a side, balance it last.
If you fix everything except one element, and it is even on one side and odd on the other, double the first number, then move on from there.

43. Problem a) CH4 + O2 ® CO2 + H2O CH4 + 2 O2 ® CO2 + 2 H2O
3) Balance the following equation.
a) CH4 + O2 ® CO2 + H2O
CH4 + 2 O2 ® CO2 + 2 H2O

44. Problem b) AgNO3 + Cu ® Cu(NO3)2 + Ag 2 AgNO3 + Cu ® Cu(NO3)2 + 2 Ag
Balance the following equation.
b) AgNO3 + Cu ® Cu(NO3)2 + Ag
2 AgNO3 + Cu ® Cu(NO3)2 + 2 Ag

45. Problem c) Mg + N2 ® Mg3N2 3 Mg + N2 ® Mg3N2
Balance the following equation.
c) Mg + N2 ® Mg3N2
3 Mg + N2 ® Mg3N2

46. Problem d) P + O2 ® P4O10 4 P + 5 O2 ® P4O10
Balance the following equation.
d) P + O2 ® P4O10
4 P + 5 O2 ® P4O10

47. Problem e) Na + H2O ® H2 + NaOH 2 Na + 2 H2O ® H2 + 2 NaOH
Balance the following equation.
e) Na + H2O ® H2 + NaOH
2 Na + 2 H2O ® H NaOH

48. Problem f) Pb(NO3)2 + K2CrO4  PbCrO4 + KNO3
Balance the following equation.
f) Pb(NO3)2 + K2CrO4  PbCrO4 + KNO3
Pb(NO3)2 + K2CrO4  PbCrO4 + 2 KNO3

49. Problem g) MnO2 + HCl  MnCl2 + H2O+ Cl2
Balance the following equation.
g) MnO2 + HCl  MnCl2 + H2O+ Cl2
MnO2 + 4 HCl  MnCl2 + 2 H2O + Cl2

50. Problem h) Ba(CN)2 + H2SO4  BaSO4 + HCN
Balance the following equation.
h) Ba(CN)2 + H2SO4  BaSO4 + HCN
Ba(CN)2 + H2SO4  BaSO4 + 2 HCN

51. Problem i) Zn(OH)2 + H3PO4  Zn3(PO4)2 + H2O
Balance the following equation.
i) Zn(OH)2 + H3PO4  Zn3(PO4)2 + H2O
3 Zn(OH)2 + 2 H3PO4  Zn3(PO4) H2O

52. Predicting the Products
Types of Reactions
Predicting the Products

53. Types of Reactions

54. Types of Reactions Reactions fall into 5 categories. Synthesis
Decomposition
Single replacement
Double replacement
Combustion

55. Synthesis Reactions
Whenever two or more substances combine to form one single product, the reaction is called a synthesis reaction.

56. Synthesis Reactions

57. Synthesis Reactions Key: M = Metal; NM = Nonmetal
a. Formation of binary compound: A + B → AB
b. Metal oxide and water: MO + H2O → base
c. Nonmetal oxide and water: (NM)O + H2O → acid

58. Synthesis Reactions a. Formation of binary compound: A + B → AB
If the synthesis reaction has two elements as reactants, just combine the elements, metals first, and criss-cross oxidation numbers if necessary. 58

59. Synthesis Reactions
Example
Mg + N2 ® 2+ 3- Mg N

60. Synthesis Reactions Mg N The charges do not add to give zero. 2+ 3- 3

61. Synthesis Reactions
Example
Mg + N2 ® Mg3N2

62. Synthesis Reactions Mg + N2 ® Mg3N2 3
Now the reaction needs to be balanced.
Mg + N2 ® Mg3N2 3

63. Synthesis Reactions b. Metal oxide and water: MO + H2O  base
A base is a metallic hydroxide. 63

64. Synthesis Reactions CaO + H2O ® Example
CaO is a metallic oxide. A metallic oxide plus water should yield a base (a metallic hydroxide).

65. Synthesis Reactions
Example
CaO + H2O ® 2+ 1- Ca OH

66. Synthesis Reactions ( ) Ca OH
The charges do not add to give zero, so you must criss-cross.
The hydroxide needs parenthesis. 2+ 1- ( ) Ca OH 1 2

67. Synthesis Reactions
Example
CaO + H2O ® Ca(OH)2

68. Synthesis Reactions CaO + H2O ® Ca(OH)2 Check the balancing.
The reaction is already balanced!

69. Synthesis Reactions c. Nonmetal oxide and water: (NM)O + H2O  acid
The acid will be a ternary acid, hydrogen with a polyatomic ion. 69

70. Synthesis Reactions SO2 + H2O ® Example
SO2 is a nonmetallic oxide. A nonmetallic oxide plus water will yield an acid, a ternary acid.

71. Synthesis Reactions SO2 + H2O ® Example
Ternary acids start with H and end in O.
The other element goes in the center.

72. Synthesis Reactions H S O SO2 + H2O ® Example
This is the only compound for which you can add the number of elements and use these numbers as subscripts.

73. Synthesis Reactions H S O SO2 + H2O ® Example 2 1 3
There are 2 hydrogens.
There is one sulfur.
There are three oxygens.

74. Synthesis Reactions SO2 + H2O ® H2SO3 Example
The reaction is balanced.

75. Problem a) Ca + Cl2 ® Ca + Cl2  CaCl2
4) Write and balance the following synthesis reaction.
a) Ca + Cl2 ®
Remember that the first step is to write the formula.
Then balance.
Ca + Cl2  CaCl2

76. Problem b) Fe + O2 ® 2 Fe + O2  2 FeO
Write and balance the following synthesis reaction.
b) Fe + O2 ®
HINT: Use iron (II).
2 Fe + O2  2 FeO

77. Problem c) K2O + H2O ® K2O + H2O  2 KOH
Write and balance the following synthesis reaction.
c) K2O + H2O ®
K2O + H2O  2 KOH

78. Problem d) Al + O2 ® 4 Al + 3 O2  2 Al2O3
Write and balance the following synthesis reaction.
d) Al + O2 ®
4 Al O2  2 Al2O3

79. Problem e) SO3 + H2O ® SO3 + H2O  H2SO4
Write and balance the following synthesis reaction.
e) SO3 + H2O ®
SO3 + H2O  H2SO4

80. Problem f) N2O5 + H2O ® N2O5 + H2O  2 HNO3
Write and balance the following synthesis reaction.
f) N2O5 + H2O ®
N2O5 + H2O  2 HNO3

81. Decomposition Reactions
decompose = fall apart
In a decomposition reaction, one compound breaks down into two or more simpler substances.

82. Decomposition Reactions

83. Decomposition Reactions
Key: M = Metal; NM = Nonmetal
a. Binary compounds:
AB → A + B
b. Metallic carbonates:
MCO3 → MO + CO2
c. Metallic hydrogen carbonates:
MHCO3 → MCO3 (s) + H2O (l) + CO2 (g) 83

84. Decomposition Reactions
Key: M = Metal; NM = Nonmetal
d. Metallic hydroxides:
MOH → MO + H2O
e. Metallic chlorates:
MClO3 → MCl + O2
f. Oxyacids decompose to nonmetal oxides and water:
acid → (NM)O + H2O 84

85. Decomposition Reactions
a. Binary compounds:
AB → A + B
A binary compound is made up of only two elements.
The compound merely falls apart into its elements. 85

86. Decomposition Reactions
H2O
H O 2 2
Both of these elements are diatomic!!!

87. Decomposition Reactions
H2O
H O 2 2
Now we must balance. 2
H2O H O2 2

88. Decomposition Reactions
HgO
Hg O 2
Oxygen is diatomic!!!

89. Decomposition Reactions
HgO
Hg O 2
Now we must balance. 2
HgO Hg + O2 2

90. Decomposition Reactions
b. Metallic carbonates:
MCO3 → MO + CO2 90

91. Example NiCO3 Write and balance the following decomposition reaction.
NiCO3 is a metallic carbonate.

92. Example NiCO3 NiCO3 is called nickel (II) carbonate.
The Chemistry Reference Tables state that a metallic carbonate decomposes to form a MO (metallic oxide) and CO2.

93. Example Ni O NiCO3 The metallic oxide is nickel (II) oxide. 2+ 2-
The two oxidation numbers add to give zero, so the formula is NiO.

94. Example NiCO3 NiO + CO2 Check the balancing.
The reaction is already balanced!

95. Decomposition Reactions
c. Metallic hydrogen carbonates:
MHCO3 → MCO3 (s) + H2O (l) + CO2 (g) 95

96. Example
Write and balance the following decomposition reaction.
Ca(HCO3)2
Ca(HCO3)2 is a metallic hydrogen carbonate. The Chemistry Reference Tables state that a metallic carbonate decomposes to form a MO (metallic oxide), water and CO2. 96

97. Example Ca O Ca(HCO3)2 The metallic oxide is calcium oxide. 2+ 2-
The two oxidation numbers add to give zero, so the formula is CaO. 97

98. Example
Ca(HCO3)2
CaO + H2O + CO2 2
Check the balancing. 98

99. Decomposition Reactions
d. Metallic hydroxides:
MOH → MO + H2O 99

100. Example KOH Write and balance the following decomposition reaction.
KOH is a base (a metallic hydroxide). The Chemistry Reference Tables state that a base decomposes to form a MO (metallic oxide) and water.
100

101. Example KOH K O The metallic oxide is calcium oxide. 1+ 2-
The two oxidation numbers DO NOT add to give zero, so you must criss-cross.
101

102. Example
KOH 2
K2O + H2O
Check the balancing.
102

103. Decomposition Reactions
e. Metallic chlorates:
MClO3 → MCl + O2
103

104. Example AgClO3 Write and balance the following decomposition reaction.
AgClO3 is a metallic chlorate. The Chemistry Reference Tables state that a base decomposes to form a metallic chloride and oxygen gas.
104

105. Example AgClO3 Ag Cl The metallic chloride is silver chloride. 1+ 1-
The two oxidation numbers add to give zero, so no criss-crossing.
105

106. Example
AgClO3 2
AgCl O2 2 3
Check the balancing.
106

107. Decomposition Reactions
f. Oxyacids decompose to nonmetal oxides and water:
acid → (NM)O + H2O
107

108. Example H3PO4 Write and balance the following decomposition reaction.
H3PO4 is an acid. The Chemistry Reference Tables state that an decomposes to form a nonmetallic oxide and water.
108

109. Example
H3PO4 2
P?O? H2O 3
Remember for acids you can “steal” subscripts.
Because the hydrogens do not balance, you have to balance them first.
109

110. Example
H3PO4 2
P O H2O ? ? 3 2 5
Now there are 2 P’s on the left and O’s on the left.
3 of the 8 oxygen’s are in the water, so that only leaves 5 more.
110

111. Example
H3PO4 2
P2O H2O 3
Check the balancing.
111

112. Problem a) KClO3 ® 2 KClO3  2 KCl + 3 O2
5) Write and balance the following decomposition reaction.
a) KClO3 ®
2 KClO3  2 KCl O2

113. Problem b) CaBr2 ® CaBr2  Ca + Br2
Write and balance the following decomposition reaction.
b) CaBr2 ®
CaBr2  Ca + Br2

114. Problem c) Li2CO3 ® Li2CO3  Li2O + CO2
Write and balance the following decomposition reaction.
c) Li2CO3 ®
Li2CO3  Li2O + CO2

115. Problem d) Cr(OH)2 ® Cr(OH)2  CrO + H2O
Write and balance the following decomposition reaction.
d) Cr(OH)2 ®
Cr(OH)2  CrO + H2O

116. Problem e) NaHCO3 ® 2 NaHCO3  Na2O + H2O + 2 CO2
Write and balance the following decomposition reaction.
e) NaHCO3 ®
2 NaHCO3 
Na2O + H2O CO2

117. Problem f) HNO2 ® 2 HNO2  N2O3 + H2O
Write and balance the following decomposition reaction.
f) HNO2 ®
Dinitrogen trioxide one of the products.
2 HNO2  N2O3 + H2O

118. Single Replacement
In a single-displacement reaction, one element takes the place of another in a compound.
One reactant must be an element and one reactant must be a compound.
The products will be a different element and a different compound.

119. Single Replacement
Remember zinc, Zn, always forms a +2 ion doesn’t need parenthesis.
In addition, silver, Ag, always forms a +1 ion.

120. Single Replacement
Some single replacement reactions do not occur because some elements are not as active as others.

121. Single Replacement
There is a list referred to as the Activity Series on page 7 of your Chemistry Reference Packet.
A higher element on the list replaces lower element.
If the element by itself is lower on the list, the reaction will NOT occur.

122. Single Replacement Reactions
Key: M = Metal; NM = Nonmetal
a. Metal-Metal replacement:
A + BC → AC + B
b. Active metal replaces H from water: M + H2O → MOH + H2
122

123. Single Replacement Reactions
Key: M = Metal; NM = Nonmetal
c. Active metal replaces H from acid:
M + HX → MX + H2
d. Halide-Halide replacement:
D + BC → BD + C
123

124. Single Replacement Reactions
a. Metal-Metal replacement:
A + BC → AC + B
You must check the activity series on page 7 of your Chemistry Reference Packet to see if this is possible.
124

125. Single Replacement
K + NaCl ®
Potassium wants to replace sodium.

126. Single Replacement K + NaCl ® YES!!
Is potassium higher than sodium on the Activity Series of Metals?
YES!!

127. Single Replacement K + NaCl ® KCl + Na
Because K is higher, potassium can replace sodium.
The potassium will bond with the chlorine and the sodium will be alone.

128. Single Replacement K + NaCl ® KCl + Na K Cl
You must always check to see if the compound formed needs criss-crossing. 1+ 1- K Cl
Since the charges add to get zero, the formula remains KCl.

129. Single Replacement K + NaCl ® KCl + Na Check for balancing.
The reaction is balanced!

130. Single Replacement Sn + FeCl3 ® Tin wants to replace iron.
You must check the activity series on page 7 of your Chemistry Reference Packet to see if this is possible.

131. Single Replacement Sn + FeCl3 ® NO!! Metals replace metals
Is tin higher than iron on the Activity Series of Metals?
NO!!

132. Single Replacement Sn + FeCl3 ® No reaction Metals replace metals
Because Sn is NOT higher, tin cannot replace iron.
No reaction occurs.

133. Single Replacement Reactions
b. Active metal replaces H from water:
M + H2O → MOH + H2
You must check the activity series on page 7 of your Chemistry Reference Packet to see if this is possible.
133

134. Single Replacement Na + H2O (cold) ® Metals replace hydrogen
Think of water as HOH.
Metals high enough on the activity series replace the first H and combine with the OH1- (hydroxide) according to page 6 of the Reference Tables.

135. Single Replacement Na + HOH (cold) ® YES!!
Is sodium above hydrogen and higher than the line marked “Replace hydrogen from cold water” on the activity series?
YES!!

136. Single Replacement Na + HOH (cold) ® NaOH + H
Sodium replaces the first H, bonding with hydroxide.

137. Single Replacement Na + H2O (cold) ® NaOH + H 2
But hydrogen is diatomic.
Now check the criss-crossing for NaOH.

138. Single Replacement Na + H2O (cold) ® NaOH + H 1+ 1- Na OH 2
No criss-crossing is needed for NaOH.

139. Single Replacement Na + H2O (cold) ® 2 2 NaOH + H 2
Now check the balancing.
The 2’s are needed to balance the hydrogen’s, but now Na is not balanced.

140. Single Replacement Na + 2H2O (cold) ® 2 2 NaOH + H 2
Now the reaction is balanced!

141. Single Replacement Reactions
c. Active metal replaces H from acid:
M + HX → MX + H2
You must check the activity series on page 7 of your Chemistry Reference Packet to see if this is possible.
141

142. Single Replacement Mg + HCl ®
Metals higher on the activity series replace the H and combine with the nonmetal according to page 6 of the Reference Tables. Hydrogen gas is a second product.

143. Single Replacement Mg + HCl ® YES!!
Is magnesium above hydrogen on the activity series?
YES!!

144. Single Replacement Mg + HCl ® MgCl + H
Magnesium replaces the H, bonding with the chloride ion.

145. Single Replacement MgCl + H Mg + HCl ® 2 But hydrogen is diatomic.
Now check the criss-crossing for MgCl.

146. Single Replacement Mg + HCl ® MgCl + H 2+ 1- Mg Cl MgCl2 2
Criss-crossing is needed.
MgCl2

147. Single Replacement Mg + HCl ® 2 MgCl2 + H 2 Now check the balancing.
The 2 is added to balance the hydrogen and the chlorine.

148. Single Replacement Reactions
d. Halide-Halide replacement:
D + BC → BD + C
You must check the activity series on page 7 of your Chemistry Reference Packet to see if this is possible.
148

149. Single Replacement Nonmetals can replace other nonmetals.
This is limited to F2 , Cl2 , Br2 , I2
The order of activity is listed in the Chemistry Reference Packet, page 7.
Higher replaces lower.

150. Single Replacement F2 + HCl ® YES!!
Is fluorine above chlorine in the activity series of halogens?
YES!!

151. Single Replacement F2 + HCl ® HF + Cl
Fluorine replaces the chlorine, bonding with hydrogen.

152. Single Replacement F2 + HCl ® HF + Cl 1+ 1- H F 2
But chlorine is diatomic.
Check the oxidation numbers of H and F. 1+ 1- H F

153. Single Replacement F2 + HCl ® HF + Cl F2 + HCl ® HF + Cl2 2 2 2
Check balancing.
F HCl ® HF + Cl2 2 2

154. Problem a) Rb + AlN ® 3 Rb + AlN  Rb3N + Al
6) Write and balance the following single replacement reaction.
a) Rb + AlN ®
3 Rb + AlN  Rb3N + Al

155. Problem b) Zn + HCl ® Zn + 2 HCl  ZnCl2 + H2
Write and balance the following single replacement reaction.
b) Zn + HCl ®
Zn HCl  ZnCl2 + H2

156. Problem c) Ag + CoBr2 ® Ag + CoBr2  no reaction
Write and balance the following single replacement reaction.
c) Ag + CoBr2 ®
Ag + CoBr2  no reaction

157. Problem d) Ag + H2O (steam) ® Ag + H2O (steam)  no reaction
Write and balance the following single replacement reaction.
d) Ag + H2O (steam) ®
Ag + H2O (steam)  no reaction

158. Problem e) Cu + H2SO4 ® Cu + H2SO4  no reaction
Write and balance the following single replacement reaction.
e) Cu + H2SO4 ®
Cu + H2SO4  no reaction

159. Problem f) Cr + H3PO4 ® 2Cr + 2H3PO4  2CrPO4 + 3H2
Write and balance the following single replacement reaction.
f) Cr + H3PO4 ®
(HINT: Use Cr3+ )
2Cr + 2H3PO4  2CrPO H2

160. Problem g) Ca + H2O (steam) ® Ca + 2H2O (steam)  Ca(OH)2 + H2
Write and balance the following single replacement reaction.
g) Ca + H2O (steam) ®
Ca + 2H2O (steam)  Ca(OH)2 + H2

161. Problem h) Br2 + KCl ® Br2 + KCl  no reaction
Write and balance the following single replacement reaction.
h) Br2 + KCl ®
Br2 + KCl  no reaction

162. Problem i) Cl2 + KI ® Cl2 + 2 KI  2 KCl + I2
Write and balance the following single replacement reaction.
i) Cl2 + KI ®
Cl KI  2 KCl + I2

163. Double Replacement
In double-displacement reactions, the positive portions of two ionic compounds are interchanged.
The reactants must be two ionic compounds or acids.
Double replacement reactions usually take place in aqueous solution.

164. Double Replacement Reactions
AB + CD → AD + CB
a. Formation of a precipitate from solution
b. Acid-Base neutralization
164

165. Double Replacement Reactions
AB + CD → AD + CB
a. Formation of a precipitate from solution
165

166. Example NaOH + FeCl3 ® The positive ions change place.
You must check to see if you need to criss-cross the products.
NaOH + FeCl3 ® Fe+3 OH- + Na+1Cl-1
NaOH + FeCl3 ® Fe(OH)3 + NaCl

167. Example NaOH + FeCl3 ® Fe(OH)3 + NaCl NaOH + FeCl3 ® Fe(OH)3 + NaCl 3
Now balance.
NaOH + FeCl3 ® Fe(OH) NaCl 3 3

168. Double Replacement
A double replacement reaction will only happen if one of the products:
doesn’t dissolve in water and forms a solid,
is a gas that bubbles out, or
is a covalent compound usually water.

169. Example 3NaOH + FeCl3 ® Fe(OH)3 + 3NaCl
None of the products are familiar gases. Both products are ionic (not covalent) because they start with metals.

170. Example 3NaOH + FeCl3 ® Fe(OH)3 + 3NaCl
We must consult the Solubility Rules on page 6 of the Chemistry Reference Tables to determine if a solid (a precipitate) is formed.

171. Example 3NaOH + FeCl3 ® Fe(OH)3 + 3NaCl
The “Soluble” side of the Solubility Rules states that Group 1 (IA) salts are soluble; therefore, NaCl is soluble and is NOT the precipitate.

172. Example 3NaOH + FeCl3 ® Fe(OH)3 + 3NaCl
The “Insoluble” side of the Solubility Rules states that all hydroxides except Group 1, Sr2+, Ba2+ and NH41+ are INSOLUBLE.
Therefore, Fe(OH)3 is the precipitate (solid).

173. Net Ionic Equations
In molecular equations, the formulas of the compounds are written as though all species existed as molecules or whole units.

174. Net Ionic Equations
An ionic equation shows dissolved ionic compounds in terms of their free ions.

175. Net Ionic Equations
Ions that are not involved in the overall reaction are called spectator ions. The net ionic equation indicates only the species that actually take part in the reaction.

176. Net Ionic Equations The following steps are useful for
writing ionic and net ionic equations:
1) Write a balanced molecular equation for the reaction.

177. Net Ionic Equations
Rewrite the equation to indicate which substances are in ionic form in solution. Remember that all soluble salts (and other strong electrolytes), are completely dissociated into cations and anions. This procedure gives us the ionic equation.

178. Net Ionic Equations
Lastly, identify and cancel spectator ions on both sides of the equation to arrive at the net ionic equation.

179. 3NaOH + FeCl3 ® Fe(OH)3 + 3NaCl
Molecular equation:
3NaOH + FeCl3 ® Fe(OH) NaCl
Complete ionic equation:
3Na+ + 3OH- + Fe3+ + 3Cl- 
Fe(OH)3 + 3Na+ + 3Cl-
Net ionic equation:
3OH- (aq) + Fe3+ (aq)  Fe(OH)3 (s)

180. Problem CaCl2 + 2 NaOH  Ca(OH)2 + 2 NaCl
7) Write and balance the following double replacement reaction. Assume the reaction takes place.
a) CaCl2 + NaOH ®
CaCl NaOH  Ca(OH) NaCl

181. Problem CaCl2 + 2 NaOH  Ca(OH)2 + 2 NaCl Ca(OH)2 is the precipitate.
Identify the precipitate and write the net ionic equation.
CaCl NaOH  Ca(OH) NaCl
Ca(OH)2 is the precipitate.
Ca OH-  Ca(OH)2

182. Problem CuCl2 + K2S  CuS + 2 KCl
Write and balance the following double replacement reaction. Assume the reaction takes place.
b) CuCl2 + K2S ®
CuCl2 + K2S  CuS KCl

183. Problem CuCl2 + K2S  CuS + 2 KCl CuS is the precipitate.
Identify the precipitate and write the net ionic equation.
CuCl2 + K2S  CuS KCl
CuS is the precipitate.
Cu S2-  CuS

184. Problem 3 KOH + Fe(NO3)3  3 KNO3 + Fe(OH)3
Write and balance the following double replacement reaction. Assume the reaction takes place.
c) KOH + Fe(NO3)3 ®
3 KOH + Fe(NO3)3  3 KNO3 + Fe(OH)3

185. Problem Fe(OH)3 is the precipitate. Fe3+ + 3OH-  Fe(OH)3
Identify the precipitate and write the net ionic equation.
3 KOH + Fe(NO3)3  3 KNO3 + Fe(OH)3
Fe(OH)3 is the precipitate.
Fe OH-  Fe(OH)3

186. Problem (NH4)2SO4 + BaF2  2 NH4F + BaSO4
Write and balance the following double replacement reaction. Assume the reaction takes place.
d) (NH4)2SO4 + BaF2 ®
(NH4)2SO4 + BaF2  2 NH4F + BaSO4

187. Problem BaSO4 is the precipitate. Ba2+ + SO42-  BaSO4
Identify the precipitate and write the net ionic equation.
(NH4)2SO4 + BaF2  2 NH4F + BaSO4
BaSO4 is the precipitate.
Ba SO42-  BaSO4

188. Double Replacement Reactions
AB + CD → AD + CB
b. Acid-Base neutralization
Remember that an acid starts with H and a base is a metallic hydroxide.
One product will be HOH (H2O).
188

189. Example H2SO3 + NaOH ® The positive ions change place.
You must check to see if you need to criss-cross the products.
H2SO3 + NaOH ® Na+1 SO3-2 + H+1OH-1
H2SO3 + NaOH ® Na2SO3 + H2O
189

190. Problem 2 HCl + Ca(OH)2  CaCl2 + 2 H2O
8. Write and balance the following double replacement reaction.
a) HCl + Ca(OH)2 ®
2 HCl + Ca(OH)2  CaCl H2O
190

191. Problem H3PO4 + 3 CuOH  Cu3PO4 + 3 H2O
8. Write and balance the following double replacement reaction.
b) H3PO4 + CuOH ®
H3PO4 + 3 CuOH  Cu3PO H2O
191

192. Combustion
A combustion reaction is one in which a substance rapidly combines with oxygen to form one or more oxides.
Combustion reactions involve a compound composed of only C and H (and maybe O) that is reacted with oxygen gas.

193. Combustion
If the combustion is complete, the products will be CO2 and H2O.
Combustion reactions produce heat, and are therefore considered exothermic reactions.

194. Combustion

195. Combustion

196. Combustion Reactions Hydrocarbon + oxygen → carbon dioxide + water
A hydrocarbon is a compound that contains both hydrogen and carbon.
196

197. Example
Complete and balance the following combustion reaction.
C4H O2 ®
CO2 + H2O
Now balance.

198. Example C4H10 + O2 ® CO2 + H2O 13/2 4 5 C4H10 + O2 ® CO2 + H2O 2 13 8
Fractions are not allowed, so multiply all coefficients by 2.
C4H O2 ® CO H2O 2 13 8 10

199. Problem a) C6H12O6 + O2 ® C6H12O6 + 6 O2  6 CO2 + 6 H2O
9) Complete and balance the following combustion reaction.
a) C6H12O6 + O2 ®
C6H12O O2  6 CO H2O

200. Problem b) C8H8 + O2 ® C8H8 + 10 O2  8 CO2 + 4 H2O
Complete and balance the following combustion reaction.
b) C8H8 + O2 ®
C8H O2  8 CO H2O

201. Problem c) C3H8O3 + O2 ® 2 C3H8O3 + 7 O2  6 CO2 + 8 H2O
Complete and balance the following combustion reaction.
c) C3H8O3 + O2 ®
2 C3H8O O2  6 CO H2O

202. How to Recognize Which Reaction Type
Look at the reactants. (E = element; C = compound)
E + E or oxide + water Synthesis
C Decomposition
E + C Single replacement
C + C Double replacement
hydrocarbon + O2 Combustion

203. Problem
Identify whether the reaction is synthesis, decomposition, single replacement, double replacement or combustion.
H2 + O2 ®
(synthesis)
H2O ®
(decomposition)

204. Problem Mg(OH)2 + H2SO3 ® HgO ®
Identify whether the reaction is synthesis, decomposition, single replacement, double replacement or combustion.
Mg(OH)2 + H2SO3 ®
(double replacement)
HgO ®
(decomposition)

205. Problem KBr + Cl2 ® Zn + H2SO4 ®
Identify whether the reaction is synthesis, decomposition, single replacement, double replacement or combustion.
KBr + Cl2 ®
(single replacement)
Zn + H2SO4 ®
(single replacement)

206. Problem AgNO3 + NaCl ® C6H6 + O2 ®
Identify whether the reaction is synthesis, decomposition, single replacement, double replacement or combustion.
AgNO3 + NaCl ®
(double replacement)
C6H6 + O2 ®
(combustion)