CHAPTER 6 – CHEMICAL REACTIONS
EVIDENCE FOR CHEMICAL CHANGE
1) Color change
2) A solid forms
3) Bubbles are formed
4) A flame is produces
5) Heat is absorbed or released
5A-1 (of 34)
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
H2
+
O2
→
H2 O
2 - H - 2
2 - O - 1
5A-3
H2
+
O2
→
H2O2
2 - H - 2
2 - O - 1
5A-4
2 H2
+
O2
→ 2 H2 O
42 - H - 2 4
2 - O - 1 2
Chemical equations are balanced by adjusting the coefficients, not by
changing the formulas of any reactant or product
5A-5
Physical states of reactants and products can be represented by
(s)
(l)
(g)
solid
liquid
gas
(aq)
dissolved in water
2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
5A-6
BALANCING CHEMICAL EQUATIONS
Mg
+ 2 HCl
→
MgCl2
1 - Mg - 1
2 1 - H - 2
2 1 - Cl - 2
5A-7
+
H2
2 HgO
→ 2 Hg
2 1 - Hg - 1 2
2 1 - O - 2
5A-8
+
O2
2 KClO3
→ 2 KCl
+ 3 O2
2 1 - K - 1 2
2 1 - Cl - 1 2
6 3 - O - 2 6
HINT: When the atoms of an element are odd and even, adjust each to a
common multiple
5A-9
CH4
+ 2 O2
→
CO2
+ 2 H2 O
1 - C - 1
4 - H - 2 4
6 2 - O - 3 4
HINT: Balance the element that appears in the most substances last
5A-10
2 NH3
+ 2½ O2
→ 2 NO
+ 3 H2O
2 1 - N - 1 2
6 3 - H - 2 6
5 2 - O - 3 4 5
4 NH3
+
5 O2
→ 4 NO
+ 6 H2O
HINT: To remove fractional coefficients, multiply all coefficients by the
denominator of the fraction
5A-11
C2H6
5A-12
+
O2
→
CO2
+
H2O
Fe(NO3)3
+ 3 NaOH
1
3
3 1
3 1
-
→
Fe
NO3
Na
OH
Fe(OH)3
-
+ 3 NaNO3
1
1 3
1 3
3
HINT: If a polyatomic ion is a reactant and a product, balance it as a single
element
5A-13
K2SO4
5A-14
+
Ba(C2H3O2)2
→
KC2H3O2
+
BaSO4
H3PO4
+
LiOH
→
Li3PO4
+
H2O
HINT: Water can be written as H(OH) to balance the hydrogens and
hydroxides separately
5A-15
H3PO4
+ 3 LiOH
OH
3
1
3 1
3 1
→
Li3PO4
+ 3 H(OH)
OH
- H - 1 3
- PO4 - 1
- Li - 3
- OH - 1 3
HINT: Water can be written as H(OH) to balance the hydrogens and
hydroxides separately
5A-16
Na
5A-17
+
H2O
→
NaOH
+
H2
2 Na
+ 2 H(OH)
OH → 2 NaOH
OH
2 1 - Na - 1 2
2 1 - H - 2
2 1 - OH - 1 2
5A-18
+
H2
CHAPTER 7b – CLASSIFICATIONS OF CHEMICAL REACTIONS
(A) Oxidation-Reduction Reactions
(1) Composition
(2) Decomposition
(3) Replacement
(4) Combustion
(B) Exchange Reactions
(5) Precipitation
(6)
5A-19
Acid-Base
OXIDATION-REDUCTION REACTION – One that transfers electrons
from one atom to another
Also called a REDOX REACTION
( A + B → AB )
(1) Composition Reactions
Mg
+
S
→
MgS
2+
5A-20
2-
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
Sodium metal reacts with chlorine gas
2 Na (s) +
Cl2 (g) →
Aluminum metal reacts with fluorine gas
5A-22
2 NaCl (s)
(2) Decomposition Reactions
( AB → A + B )
Mercury (II) oxide is heated
2 HgO (s) →
2 Hg (l) +
O2 (g)
Electricity is passed through molten sodium chloride
5A-23
(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
3 Mg (s) +
Fe2O3 (s) →
3 MgO (s) +
Iron is heated with magnesium oxide
No Reaction
5A-24
2 Fe (s)
Active elemental nonmetals react with less active nonmetal ions
Chlorine gas is bubbled through a sodium bromide solution
Cl2 (g) +
2 NaBr (aq) → 2 NaCl (aq) +
Liquid bromine is poured into a sodium chloride solution
No Reaction
5A-25
Br2 (l)
Most metals (except the Noble Metals) will react with the hydrogen ions
from acids
Zinc metal reacts with hydrochloric acid
Zn (s) +
2 HCl (aq) →
ZnCl2 (aq) +
Copper metal reacts with hydrochloric acid
No Reaction
5A-26
H2 (g)
Alkali metals (and Alkaline Earth metals below Mg) will react with the
hydrogen from water
Sodium metal reacts with water
Na
5A-27
+
H 2O
→
Alkali metals (and Alkaline Earth metals below Mg) will react with the
hydrogen from water
Sodium metal reacts with water
2 Na (s) +
5A-28
2 H(OH) (aq) → 2 NaOH (aq) +
H2 (g)
(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 (g) +
5A-29
2 O2 (g) →
CO2 (g) +
2 H2O (g)
Octane (C8H18) burns in air
C8H18
+ 12½ O2
2 C8H18 (l) +
5A-30
→
8 CO2
+
9 H2O
25 O2 (g) → 16 CO2 (g) + 18 H2O(g)
Octane (C8H18) burns in air
C8H18
+ 12½ O2
2 C8H18 (l) +
5A-30
→
8 CO2
+
9 H2O
25 O2 (g) → 16 CO2 (g) + 18 H2O (g)
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
Solutions of lead (II) nitrate and sodium iodide are mixed
Pb(NO3)2 (aq) +
2 NaI (aq)
→
PbI2(s)
+
2 NaNO3(aq)
Solutions of barium chloride and potassium sulfate are mixed
5A-32
(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 (aq) +
NaOH (aq)
→
HOH (l)
+
NaCl (aq)
Solutions of sulfuric acid and potassium hydroxide are mixed
5A-33