Chemical Equations and Reactions

1
Chapter 8

• Chemical Equations and Reactions

2
Types of Chemical Reactions

• Direct Combination
• (Synthesis)

A B ? AB
AB ? A B

• Decomposition

• Single Replacement

A(metal) BC ? B AC
A(Nonmetal) BC ? C BA

• Double Replacement

AB CD ? CB AD
AB CD ? AD CB

• Combustion

C?H?(g) O2(g) ? CO2(g) H2O(g)
3
Direct Combination (Also called Synthesis or
Composition Reactions)
Two or more substances combine to form a new
compound.
A B ? AB

• Reaction of elements with oxygen and sulfur
• Reactions of metals with Halogens
• Synthesis Reactions with Oxides
• There are others not covered here!

 Formation of Water
4
Direct Combination
Two or more substances combine to form a new
compound.
A B ? AB
Combination reactions with oxygen or sulfur
CO2
C O2 ? ________
2
H2O
2
H2 O2 ? ________
FeS
Fe S ? ________ iron(II) sulfide
S
3
Fe ___ ? Fe2S3 iron(III) sulfide
2
5
Direct Combination
Two or more substances combine to form a new
compound.
A B ? AB
Combination reactions of metals with halogens
NaCl
2
Na Cl2 ? ________
2
Ions would be Na and Cl-
AlF3
2
Al F2 ? ________
3
2
Ions would be Al3 and F-
6
Direct Combination
Two or more substances combine to form a new
compound.
A B ? AB
Combination reactions of nonmetal oxides with
water
H2SO4
SO3 H2O ? ________
Form acid with ions H and SO42-
H2SO3
SO2 H2O ? ________
Form acid with ions H and SO32-
7
Direct Combination
Two or more substances combine to form a new
compound.
A B ? AB
Combination reactions of metal oxides with water
Ca(OH)2
CaO HOH ? ________
Form base with ions Ca2 and OH-1
NaOH
2
Na2O HOH ? ________
Form base with ions Na and OH-
8
Direct Combination
Two or more substances combine to form a new
compound.
A B ? AB
Mg(s) O2 (g) ? MgO(s)
2
2
9
Balancing Reactions
The Law of Conservation of Mass states Matter is
neither created nor destroyed in ordinary
chemical reactions.

• Reactants Products
• Mass is conserved.
• Number of atoms is conserved.

10
Balancing Reactions
When Balancing Chemical Reactions

• Formulas CANNOT change.

H2, N2,O2,F2 Cl2 Br2 I2

• You MUST know 7 diatomic molecules

• Use coefficients to balance the number of atoms.

H2(g) O2(g) ? H2O(g)
2
2
Each side of the arrow has 4 Hs and 2 Os.
11
Balancing Reactions

• To the Website!
• Link (Chembalancer)
• Link (Sciencegeek.net)

12
Decomposition Reactions
A single compound undergoes a reaction that
produces two or more simpler substances
AB ? A B

• Decomposition of
• Binary compounds (Nitrogen Triiodide)

NI3 (s)
NI3 (s) ? N2 (g) I2 (g)
3
2
Purple Gas
Dark Brown Solid
Invisible gas
13
Decomposition Reactions
A single compound undergoes a reaction that
produces two or more simpler substances
AB ? A B

• Decomposition of
• Binary compounds (Lab 10 Copper(II) Chloride)

electrolysis
CuCl2 (aq) ? Cu(s) Cl2 (g)
Bubbles that have distinct odor
Blue liquid
Reddish solid
Cu2
2Cl1-
14
Oxidation and Reduction (Redox)

• Electrons are transferred

• Spontaneous redox rxns can transfer energy
• Electrons (electricity)
• Heat

• Non-spontaneous redox rxns can be made to happen
  with electricity

15
Oxidation and Reduction
An old memory device for oxidation and reduction
goes like this
LEO says GER
Lose Electrons Oxidation
Gain Electrons Reduction
16
Decomposition Reactions
A single compound undergoes a reaction that
produces two or more simpler substances
AB ? A B
Usually occur by adding energy
?
elect.
Heat
or
Catalysts are added to speed up a reaction
Pt
MnO2
Double arrows indicate the reaction can go both
directions
17
Other Decomposition Reactions
A single compound undergoes a reaction that
produces two or more simpler substances
AB ? A B

• Decomposition of
• Binary compounds 2AlCl3 (s) ? 2Al (g) 3Cl2
  (g)
• Metal carbonates CaCO3 (s) ? CaO (s) CO2 (g)
• Metal hydroxides Ca(OH)2 (s) ? CaO (s) H2O
  (g)
• Metal chlorates 2KClO3 (s) ? 2KCl (s) 3O2
  (g)
• Oxyacids H2CO3 (aq) ? CO2 (g) H2O
  (l)

18
Single Replacement Reactions

• Lithium
• Potassium
• Calcium
• Sodium
• Magnesium
• Aluminum
• Zinc
• Chromium
• Iron
• Nickel
• Lead
• Hydrogen
• Bismuth
• Copper
• Mercury
• Silver
• Platinum
• Gold

A(metal) BC ? B AC
Replacement of

• Metals cations by another metal

Ni CuCl2 ?
Cu NiCl2

• Hydrogen in water by a metal

Nickel
Na HOH ?
H2 NaOH
2
2
2

• Hydrogen in an acid by a metal

Copper
Zn HCl ?
H2 ZnCl2
2
19
Single Replacement Reactions

• Lithium
• Potassium
• Calcium
• Sodium
• Magnesium
• Aluminum
• Zinc
• Chromium
• Iron
• Nickel
• Lead
• Hydrogen
• Bismuth
• Copper
• Mercury
• Silver
• Platinum
• Gold

A(metal) BC ? B AC
A(Nonmetal) BC ? C BA

• Fluorine
• Chlorine
• Bromine
• Iodine

Replacement of

• Halogen anions by more active halogens

F2 HCl ?
Cl2 HF
2
2
20
The Activity Series of the Metals

• Lithium
• Potassium
• Calcium
• Sodium
• Magnesium
• Aluminum
• Zinc
• Chromium
• Iron
• Nickel
• Lead
• Hydrogen
• Bismuth
• Copper
• Mercury
• Silver
• Platinum
• Gold

Metals can replace other metals provided that
they are above the metal that they are trying to
replace.
Zn CuCl2 ?
Cu ZnCl2
Zn NaCl ?
No Reaction
Metals above hydrogen can replace hydrogen in
acids.
Fe HCl ?
H2 FeCl3
6
2
2
3
Metals from sodium upward can replace hydrogen in
water
K HOH ?
H2 KOH
2
2
2
21
The Activity Series of the Halogens

• Fluorine
• Chlorine
• Bromine
• Iodine

Halogens can replace other halogens in
compounds, provided that they are above the
halogen that they are trying to replace.
2NaCl(s) F2(g) ?
2NaF(s) Cl2(g)
???
MgCl2(s) Br2(g) ?
???
No Reaction
22
Double Replacement Reactions
The ions of two compounds exchange places in
an aqueous solution to form two new compounds.
AB CD ? CB AD
AB CD ? AD CB
Same result!
One of the compounds formed is usually a
precipitate, an insoluble gas that bubbles out
of solution, or a molecular compound, usually
water.
23
Combustion Reactions
A substance combines with oxygen, releasing a
large amount of energy in the form of light and
heat.

• The burning of natural gas, wood, gasoline

CxHy(g) O2(g) ? CO2(g) H2O(g)
C3H8(g) O2(g) ? CO2(g) H2O(g)
3
4
5

• Reactive elements combine with oxygen

P4(s) O2(g) ? P4O10(s)
5
(This is also a direct combination reaction)