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1Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Chapter 6 Chemical Reactions
6.1 Chemical Changes
6.2 Chemical Equations
6.3 Balancing a Chemical Equation
2Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The physicalproperties of asubstance are thecharacteristicswe can observeor measurewithout changingthe substance.
Physical Properties
3Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In a physical change,
The identity and composition of thesubstance do not change.
The state can change or the material canbe torn into smaller pieces.
In a chemical change,
New substances form with differentcompositions and properties.
A chemical reaction takes place.
Physical and Chemical Change
4Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Physical and Chemical Change
2
5Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Some Examples of Chemical andPhysical Changes
6Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Classify each of the following as a
1) physical change or 2) chemical change
A. ____ Burning a candle.
B. ____ Ice melting on the street.
C. ____ Toasting a marshmallow.
D. ____ Cutting a pizza.
E. ____ Polishing a silver bowl.
Learning Check
7Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Classify each of the following as a
1) physical change or 2) chemical change
A. 2 Burning a candle.
B. 1 Ice melting on the street.
C. 2 Toasting a marshmallow.
D. 1 Cutting a pizza.
E. 2 Polishing a silver bowl.
Solution
8Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Chemical Reaction
In a chemicalreaction, achemical changeproduces one ormore newsubstances.
During a reaction,old bonds arebroken and newbonds are formed.
3
9Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In a chemical reaction,atoms in the reactantsare rearranged to formone or more differentsubstances.
In this reaction, Fe andO2 react to form rust(Fe2O3).
4Fe + 3O2 2Fe2O3
Chemical Reaction
10Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A chemical equation Shows the chemical formulas of the reactants to the
left of an arrow and the products on the right. Reactants ProductsMgO + C CO + Mg
Can be read in words. “Magnesium oxide reactswith carbon to form carbon monoxide andmagnesium.”
Writing a Chemical Equation
11Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Symbols Used in Equations
Symbols usedin equationsshow the statesof the reactantsand productsand thereactionconditions.
12Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
4 NH3 + 5 O2 4 NO + 6 H2O
Four molecules of NH3 react with fivemolecules of O2 to produce four moleculesof NO and six molecules of H2O.
orFour moles of NH3 react with 5 moles of O2to produce four moles of NO and six molesof H2O.
Quantities in A Chemical Reaction
4
13Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In any ordinary chemical reaction, matter is notcreated nor destroyed.
+ + H2 + Cl2 2 HCl
Total atoms = Total atoms 2 H, 2 Cl 2H, 2 Cl
Total Mass = Total Mass2(1.0) + 2(35.5) 2(36.5)73.0 g = 73.0 g
Law of Conservation of Mass
14Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Balancing a Chemical Equation
A chemical equation is balanced when thereare the same numbers of each type of atomon both sides of the equation.
Al + S Al2S3 Not Balanced
2Al + 3S Al2S3 Balanced
15Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
To balance an equation, place coefficients in front ofthe appropriate formulas.4 NH3 + 5 O2 4 NO + 6 H2O
Check the balance by counting the atoms of eachelement in the reactants and the products.
4 N (4 x 1N) = 4 N (4 x 1N)12 H (4 x 3H) = 12 H (6 x 2H)10 O (5 x 2O) = 10 O (4O + 6O)
Using Coefficients to Balance
16Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Balance one element at a time.
Use only coefficients to balance.
Fe3O4 + H2 Fe + H2O
Fe: Fe3O4 + H2 3Fe + H2O
O: Fe3O4 + H2 3Fe + 4H2O
H: Fe3O4 + 4H2 3Fe + 4H2O
Steps in Balancing an Equation
5
17Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Check the balance of atoms in the following: Fe3O4 + 4 H2 3 Fe + 4 H2O
A. Number of H atoms in products.
1) 2 2) 4 3) 8
B. Number of O atoms in reactants.
1) 2 2) 4 3) 8
C. Number of Fe atoms in reactants.
1) 1 2) 3 3) 4
Learning Check
18Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Fe3O4 + 4 H2 3 Fe + 4 H2O
A. Number of H atoms in products.
3) 8 (4H2O)
B. Number of O atoms in reactants.
2) 4 (Fe3O4)
C. Number of Fe atoms in reactants.
2) 3 (Fe3O4)
Solution
19Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Balancing with Polyatomic Ions
Polyatomic ions can be balanced as a unit whenthey appear on both sides.Pb(NO3)2 + NaCl NaNO3 + PbCl2
Balance NO3- as a unit
Pb(NO3)2 + NaCl 2NaNO3 + PbCl2
2 NO3– = 2 NO3
–
Balance Na (or Cl)Pb(NO3)2 + 2NaCl 2NaNO3 + PbCl2
2Na+ = 2Na+
2Cl– = 2Cl–20Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Balance each equation. The coefficients in theanswers are read from left to right.
A. __Mg + __N2 __Mg3N2
1) 1, 3, 2 2) 3, 1, 2 3) 3, 1, 1
B.__Al + __Cl2 __AlCl3
1) 3, 3, 2 2) 1, 3, 1 3) 2, 3, 2
Learning Check
6
21Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A. 3) 3, 1, 1 3 Mg + 1 N2 1 Mg3N2
B. 3) 2, 3, 2 2 Al + 3 Cl2 2 AlCl3
Solution
22Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A. __Fe2O3 + __C __Fe + __CO2
1) 2, 3, 2,3 2) 2, 3, 4, 3 3) 1, 1, 2, 3
B. __Al + __FeO __Fe + __Al2O3
1) 2, 3, 3, 1 2) 2, 1, 1, 1 3) 3, 3, 3, 1
C. __Al + __H2SO4 __Al2(SO4)3 + __H2
1) 3, 2, 1, 2 2) 2, 3, 1, 3 3) 2, 3, 2, 3
Learning Check
23Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A. 2) 2, 3, 4, 3 2 Fe2O3 + 3 C 4 Fe + 3 CO2
B. 1) 2, 3, 3, 1 2 Al + 3 FeO 3 Fe + 1 Al2O3
C. 2) 2, 3, 1, 3 2 Al + 3 H2SO4 1 Al2(SO4)3 + 3 H2
Solution
24Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
6.4 Types of Reactions
Chapter 6 Chemical Reactions
7
25Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Chemical reactions are classified intogeneral types:
Combination Decomposition Single Replacement Double Replacement Combustion
Types of Reactions
26Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In a combination reaction, two or moreelements or simple compounds combine toform one product.A + B AB
ExamplesH2 + Cl2 2HCl
2S + 3O2 2SO3
4Fe + 3O2 2Fe2O3
Combination Reactions
27Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In a combination reaction, magnesium andoxygen react to form magnesium oxide.2Mg + O2 2MgO
Combination Reactions
Mg
O2
MgO
28Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In a decomposition reaction, one substance isbroken down (split) into two or more simplersubstances.
AB A + B
2HgO 2Hg + O2
2KClO3 2KCl + 3 O2
Decomposition Reactions
8
29Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Classify the following reactions as
1) combination or 2) decomposition:
___A. H2 + Br2 2HBr
___B. Al2(CO3)3 Al2O3 + 3CO2
___C. 4 Al + 3C Al4C3
Learning Check
30Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Classify the following reactions as
1) combination or 2) decomposition:
1 A. H2 + Br2 2HBr
2 B. Al2(CO3)3 Al2O3 + 3CO2
1 C. 4 Al + 3C Al4C3
Solution
31Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In a single replacement, one element takes theplace of an element in a reacting compound.A + BC AC + BZn(s) + HCl(aq) ZnCl2(aq) + H2(g)
Single Replacement
Zn HCl
H2
ZnCl2
32Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In a double replacement, the positive ions inthe reacting compounds switch places.
AB + CD AD + CB
AgNO3 + NaCl AgCl + NaNO3
ZnS + 2HCl ZnCl2 + H2S
Double Replacement
9
33Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Example of a Double Replacement
When solutions of sodium sulfate and bariumchloride are mixed, solid BaSO4 is produced.
BaCl2 + Na2SO4 BaSO4 + 2NaCl
BaSO4
34Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Classify each of the following reactions as a
1) single replacement or 2) double replacement
__A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2
__B. Na2SO4 + 2AgNO3 Ag2SO4 + 2NaNO3
__C. 3C + Fe2O3 2Fe + 3CO
Learning Check
35Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Classify each of the following reactions as a
1) single replacement or 2) double replacement
1 A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2
2 B. Na2SO4 + 2AgNO3 Ag2SO4 + 2NaNO3
1 C. 3C + Fe2O3 2Fe + 3CO
Solution
36Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In a combustion reaction, a reactant oftencontaining carbon reacts with oxygen O2.
C + O2 CO2
CH4 + 2O2 CO2 + 2H2O
C3H8 + 5O2 3CO2 + 4H2O
Many combustion reactions utilize fuels thatare burned in oxygen to produce CO2, H2O,and energy.
Combustion
10
37Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Balance the combustion equation:
___C5H12 + ___O2 ___CO2 + ___H2O
Learning Check
38Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Balance the combustion equation:
1 C5H12 + 8 O2 5 CO2 + 6 H2O
Solution
39Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Summary of Reaction Types
40Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning Check
Identify each reaction as 1) combination 2) decomposition 3) combustion4) single replacement 5) double replacementA. 3Ba + N2 Ba3N2
B. 2Ag + H2S Ag2S + H2
C. SiO2 + 4HF SiF4 + 2H2O
D. PbCl2 + K2SO4 2KCl + PbSO4
E. K2CO3 K2O + CO2
F. C2H4 + 3O2 2CO2 + 2H2O
11
41Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Solution
Identify each reaction as 1) combination 2) decomposition 3) combustion4) single replacement 5) double replacement 1 A. 3Ba + N2 Ba3N2
4 B. 2Ag + H2S Ag2S + H2
5 C. SiO2 + 4HF SiF4 + 2H2O 5 D. PbCl2 + K2SO4 2KCl + PbSO4
2 E. K2CO3 K2O + CO2
3 F. C2H4 + 3O2 2CO2 + 2H2O