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Chapter 8
Chemical
Equations
and
Reactions
8-1 Describing Chemical Reactions
Chemical reaction – process by which one
or more substances are changed into one
or more different substances
 Reactants – starting substances
 Products – ending substances
 Conservation of mass tells us that the
mass of the reactants must be equal to the
mass of the products

8-1 Chemical Equations

Chemical equation – represents (with symbols and
formulas) the identities and relative amounts of the
reactants and products in a chemical reaction
8-1 Signs of a Chemical Reaction
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Evolution of heat and light
Production of a
gas/bubbles
Formation of a precipitate
Color change
8-1 Requirements for Properly
Written Chemical Equations
All reactants and products must be
represented
 Correct symbols and formulas must be
used for all substances in the equation
(remember diatomics!)
 Reactants on left, products on right
 Arrow means “yields” or “forms”
 Law of conservation of matter must be
satisfied – equations must be BALANCED

8-1 Balancing Chemical Equations
Equations must be balanced to show the
same number of atoms of each type on
both sides of the equation
 Balance equations by writing coefficients
 Coefficient – a small whole number that
appears in front of a formula in a chemical
equation
 NEVER change subscripts!

8-1 Balancing Equations
Write a balanced chemical equation for the
formation of ammonia from its elements.
8-1 Balancing Chemical Equations
Write a balanced chemical equation for the
decomposition of sodium chloride to its
elements.
8-1 Word and Formula Equations
It is often helpful to begin by writing a word
equation that represents all the facts about
a chemical reaction.
 In a word equation, reactants and products
are represented by words.

methane + oxygen  carbon dioxide + water
8-1 Word and Formula Equations

A formula equation represents the
reactants and products of a chemical
reaction by their symbols or formulas.
CH4 + O2  CO2 + H2O (unbalanced)
8-1 Additional Symbols Used in
Chemical Equations

(s)
(l)
(aq)
(g)
Yields
Solid
Liquid
Aqueous
gas
8-1 Reversible Reactions
A reversible reaction is one in which
products can re-form the original reactants
3Fe(s) + 4H2O(g)
Fe3O4(s) + 4H2(g)
8-1 Reactions Requiring Heat

Some reactions will only
proceed if the reactants
are heated.
2HgO(s)  2Hg(l) + O2(g)
8-1 Practice
Translate the following into a sentence:
2NaOH(aq) + MgCl2(aq)  2NaCl(aq) + Mg(OH)2(s)
NaCl(aq) + AgNO3(aq)  NaNO3(aq) + AgCl(s)
8-1 Practice
Write a balanced chemical equation for the
following processes:
Solid calcium reacts with solid sulfur to
produce solid calcium sulfide.
Hydrogen gas reacts with fluorine gas to
produce hydrogen fluoride gas.
8-2 Types of Chemical Reactions
Using generalizations about the ways
various substances interact with each
other, we can predict the products of
reactions
 There are five main types of chemical
reactions.

8-2 Types of Chemical Reactions
Synthesis
 Decomposition
 Single replacement
 Double replacement
 Combustion (of hydrocarbons)

8-2 Synthesis Reactions

Two or more substances react to form one
new compound
A + X  AX
Recognize by SINGLE PRODUCT
8-2 Synthesis Reactions
Reactions of elements with oxygen or
sulfur FORM OXIDES OR SULFIDES
 Magnesium reacts with oxygen

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Barium reacts with sulfur

Rubidium reacts with sulfur
8-2 Synthesis Reactions
Reactions of metals with halogens FORM
METAL HALIDES
 Sodium reacts with chlorine

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Potassium reacts with iodine

Magnesium reacts with fluorine
8-2 Synthesis Reactions
Metal oxides react with water to form
metal hydroxides
 Calcium oxide reacts with water
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Magnesium oxide reacts with water
8-2 Synthesis Reactions
Nonmetal oxides react with water to form
acids
 Sulfur dioxide reacts with water
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Carbon dioxide reacts with water
8-2 Decomposition Reactions
A single compound breaks down to
produce two or more simpler substances
AX  A + X
Recognize by single reactant
Often require energy in the form of heat,
light or electricity.

8-2 Decomposition Reactions
Decomposition of binary compounds
produces elements
 Decomposition of water
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Decomposition of sodium chloride
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Decomposition of magnesium mercury (II)
oxide
8-2 Decomposition Reactions
Decomposition of metal carbonates
FORMS METAL OXIDE AND CARBON
DIOXIDE
 Decomposition of calcium carbonate
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Decomposition of magnesium carbonate
8-2 Decomposition Reactions
Decomposition of metal hydroxides
FORMS METAL OXIDES AND WATER
 Decomposition of calcium hydroxide
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Decomposition of copper (II) hydroxide
8-2 Decomposition Reactions
Decomposition of metal chlorates FORMS
METAL CHLORIDES AND OXYGEN
 Decomposition of potassium chlorate
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Decomposition of sodium chlorate
8-2 Decomposition Reactions
Decomposition of acids PRODUCES
NONMETAL OXIDES AND WATER
 Decomposition of carbonic acid
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Decomposition of sulfuric acid
8-2 Single Replacement Reactions

One element replaces another similar
element in a compound
A + BX  AX + B
OR
Y + BX  BY + X
8-2 Single Replacement Reactions
Replacement of a metal by another metal
 Aluminum reacts with lead nitrate

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Sodium reacts with iron (II) chloride

Calcium reacts with aluminum phosphate
8-2 Single Replacement Reactions
Replacement of hydrogen by a metal
 Sodium reacts with water

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Magnesium reacts with hydrochloric acid

Calcium reacts with nitric acid
8-2 Single Replacement Reactions
Replacement of Halogens
 Chlorine reacts with potassium bromide

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Fluorine reacts with sodium chloride

Fluorine reacts with potassium iodide
8-3 Activity Series of the Elements
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An activity series is a list of elements organized
according to the ease with which the elements
undergo certain chemical reactions
For metals, greater activity means greater ease
of LOSS OF ELECTRONS to form cations.
For nonmetals, greater activity means greater
ease of GAIN OF ELECTRONS to form anions.
An activity series can be used to determine
whether or not a single replacement reaction will
take place.
8-3 Activity Series
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More active metals are
HIGHER on the list.
A more active metal can
replace a less active
metal on the activity
series.
Example: Na + CoCl2 
Example: Cu + AlCl3 
Example: Cr + HCl 
Example: Au + MgSO4 
8-3 Activity Series
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Example: Cl2 + NaBr 
Example: Br2 + KF 
Example: Cl2 + MgBr2 
8-2 Double Replacement Reactions
The ions of two compounds exchange
places to form two new compounds
 One of the products is usually a
precipitate, gas or molecular compound
(like water)
AX + BY  AY + BX

8-2 Double Replacement Reactions
Formation of a precipitate
 Potassium iodide reacts with lead (II)
nitrate

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Magnesium chloride reacts with sodium
hydroxide
8-2 Double Replacement Reactions
Formation of a gas
 Iron (II) sulfide reacts with hydrochloric
acid

8-2 Double Replacement Reactions
Formation of water
 An acid reacts with a base – also called a
NEUTRALIZATION reaction
 Hydrochloric acid reacts with sodium
hydroxide
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Sulfuric acid reacts with potassium
hydroxide
8-2 Combustion Reactions
A substance combines with oxygen,
releasing a large amount of energy in the
form of light and heat
 Hydrocarbons burn in oxygen
 A hydrocarbon is a compound composed
of hydrogen and carbon

8-2 Combustion Reactions
Combustion of hydrocarbons
 When a hydrocarbon reacts with oxygen,
the products are carbon dioxide and water
 Combustion of butane
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Combustion of heptane
8-2 Simple Hydrocarbons (CnH2n+2)
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CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
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methane
ethane
propane
butane
pentane
hexane
heptane
octane
nonane
decane
It’s over!