CHAPTER 6 CHEMICAL REACTIONS

1
CHAPTER 6 CHEMICAL REACTIONS

• EVIDENCE FOR CHEMICAL CHANGE
• Color change
• A solid forms
• Bubbles are formed
• A flame is produces
• Heat is absorbed or released

5A-1 (of 34)
2
CHEMICAL EQUATION A representation of a
chemical reaction using elemental symbols and
chemical formulas
Hydrogen gas and oxygen gas produce water when
sparked
H2 O2 ? H2O
? Yields
REACTANTS Sustances on the left PRODUCTS
Substances on the right
In a chemical reaction, atoms are neither created
nor destroyed All atoms of the reactants must be
accounted for in the products Satisfying this is
called BALANCING THE EQUATION
5A-2
3
H2 O2 ? H2O
2 - H - 2 2 - O - 1
5A-3
4
H2 O2 ? H2O
2
2 - H - 2 2 - O - 1
5A-4
5
H2 O2 ? H2O
2
2
2 - H - 2 2 - O - 1
4
4
2
Chemical equations are balanced by adjusting the
coefficients, not by changing the formulas of any
reactant or product
5A-5
6
Physical states of reactants and products can be
represented by (s) solid (l) liquid (g) gas (a
q) dissolved in water
2Na (s) 2H2O (l) ? 2NaOH (aq) H2 (g)
5A-6
7
BALANCING CHEMICAL EQUATIONS
Mg HCl ? MgCl2 H2
2
1 - Mg - 1 1 - H - 2 1 - Cl - 2
2
2
5A-7
8
HgO ? Hg O2
2
2
1 - Hg - 1 1 - O - 2
2
2
2
5A-8
9
KClO3 ? KCl O2
2
3
2
1 - K - 1 1 - Cl - 1 3 - O - 2
2
2
2
2
6
6
HINT When the atoms of an element are odd and
even, adjust each to a common multiple
5A-9
10
CH4 O2 ? CO2 H2O
2
2
1 - C - 1 4 - H - 2 2 - O - 3
4
4
6
HINT Balance the element that appears in the
most substances last
5A-10
11
NH3 O2 ? NO H2O
3
2
2
2½
1 - N - 1 3 - H - 2 2 - O - 3
2
2
6
6
4
5
5
NH3 O2 ? NO H2O
6
4
4
5
HINT To remove fractional coefficients, multiply
all coefficients by the denominator of the
fraction
5A-11
12
C2H6 O2 ? CO2 H2O
5A-12
13
Fe(NO3)3 NaOH ? Fe(OH)3
NaNO3
3
3
1 - Fe - 1 3 - NO3 - 1 1 - Na - 1 1
- OH - 3
3
3
3
3
HINT If a polyatomic ion is a reactant and a
product, balance it as a single element
5A-13
14
K2SO4 Ba(C2H3O2)2 ? KC2H3O2
BaSO4
5A-14
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H3PO4 LiOH ?
Li3PO4 H2O
H2O
HINT Water can be written as H(OH) to balance
the hydrogens and hydroxides separately
5A-15
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H3PO4 LiOH ? Li3PO4
H(OH)
H
OH
OH
3
3
3 - H - 1 1 - PO4 - 1 1 - Li - 3 1
- OH - 1
3
3
3
3
HINT Water can be written as H(OH) to balance
the hydrogens and hydroxides separately
5A-16
17
Na H2O ?
NaOH H2
H2O
5A-17
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Na ? NaOH
H2
H(OH)
H
OH
OH
2
2
2
1 - Na - 1 1 - H - 2 1 - OH - 1
2
2
2
2
2
5A-18
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CHAPTER 7b CLASSIFICATIONS OF CHEMICAL REACTIONS
(A) Oxidation-Reduction Reactions (1) Compositio
n (2) Decomposition (3) Replacement (4) Comb
ustion (B) Exchange Reactions (5) Precipitation
(6) Acid-Base
5A-19
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OXIDATION-REDUCTION REACTION One that transfers
electrons from one atom to another Also called a
REDOX REACTION
(1) Composition Reactions Mg S ?
( A B ? AB )
MgS
2-
2
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Mg ? Mg2 2e- OXIDATION Losing
electrons 2e- S ? S2- REDUCTION
Gaining electrons
LEO says GER
Metals and nonmetals react to form ionic
compounds by transferring e-s form metal to
nonmetal
5A-21
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Sodium metal reacts with chlorine gas
Na Cl2
?
NaCl
2
2
(s)
(g)
(s)
Aluminum metal reacts with fluorine gas
5A-22
23
(2) Decomposition Reactions
( AB ? A B )
Mercury (II) oxide is heated
HgO ?
Hg O2
2
2
(s)
(l)
(g)
Electricity is passed through molten sodium
chloride
5A-23
24
(3) Replacement Reactions
( A BX ? AX B )
Replacement reactions occur when the elemental
reactant (A) is more active than the element in
the compound (B)
Active elemental metals react with less active
metal ions
Magnesium metal is heated with iron (III) oxide
Mg Fe2O3
?
MgO Fe
2
3
(s)
(s)
(s)
3
(s)
Iron is heated with magnesium oxide
No Reaction
5A-24
25
Active elemental nonmetals react with less active
nonmetal ions
Chlorine gas is bubbled through a sodium bromide
solution
Cl2 NaBr
?
NaCl Br2
2
2
(g)
(aq)
(aq)
(l)
Liquid bromine is poured into a sodium chloride
solution
No Reaction
5A-25
26
Most metals (except the Noble Metals) will react
with the hydrogen ions from acids
Zinc metal reacts with hydrochloric acid
Zn HCl
?
ZnCl2 H2
2
(s)
(aq)
(aq)
(g)
Copper metal reacts with hydrochloric acid
No Reaction
5A-26
27
Alkali metals (and Alkaline Earth metals below
Mg) will react with the hydrogen from water
Sodium metal reacts with water
Na H2O
?
5A-27
28
Alkali metals (and Alkaline Earth metals below
Mg) will react with the hydrogen from water
Sodium metal reacts with water
2
(aq)
2
H(OH)
Na ?
NaOH H2
2
(s)
(aq)
(g)
5A-28
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(4) Combustion Reactions
( AB O2 ? AO BO )
Combustion or burning means REACTS WITH OXYGEN
Combustion makes oxide compounds of each element
in the compound burned
Methane burns in air
CH4 O2
?
CO2 H2O
2
2
(g)
(g)
(g)
(g)
5A-29
30
Octane (C8H18) burns in air
C8H18 O2
?
CO2 H2O
9
12½
8
C8H18 O2
?
CO2 H2O
18
25
(l)
(g)
(g)
(g)
16
2
5A-30
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Octane (C8H18) burns in air
C8H18 O2
?
CO2 H2O
9
12½
8
C8H18 O2
?
CO2 H2O
18
25
(l)
(g)
(g)
(g)
16
2
5A-30
32
EXCHANGE REACTION One in which ions in two
compounds rearrange their bonding
(5) Precipitation Reactions
( AX BY ? AY BX )
Ions in solution rearrange to produce an
insoluble product
PRECIPITATE A solid formed when two solutions
are mixed
5A-31
33
Solutions of lead (II) nitrate and sodium iodide
are mixed
Pb(NO3)2 NaI ?
PbI2 NaNO3
2
2
(aq)
(aq)
(s)
(aq)
Solutions of barium chloride and potassium
sulfate are mixed
5A-32
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(6) Acid-Base Reactions
( HX AOH ? HOH AX )
Ions in solution rearrange to produce water
Solutions of hydrochloric acid and sodium
hydroxide are mixed
HCl NaOH ?
HOH NaCl
(aq)
(aq)
(l)
(aq)
Solutions of sulfuric acid and potassium
hydroxide are mixed
5A-33