UNIT 2: Chemical Reactions
Chapter 3: Chemical Names, Formulas,
and Equations
Chapter 4: Classifying Compounds
and Chemical Reactions
UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Chapter 4: Classifying Compounds and
Chemical Reactions
Airbags on motorcycles are a fairly recent safety innovation,
but airbags have been in cars since the 1980s. Airbags inflate
when a chemical reaction occurs, and a gas is produced.
What are some of the properties
that the reactants must have to be
useful in airbags?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.1
4.1 Types of Chemical Reactions
Chemists have developed a classification system for chemical
reactions using the following categories:
• combination reactions
• decomposition reactions
• single replacement reactions
• double replacement reactions
• combustion reactions
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Potassium reacts with water to
produce potassium hydroxide
and hydrogen gas.
UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.1
Combination Reactions
• A combination reaction is a chemical reaction in which two
or more reactants combine to form one new product.
• A combination reaction can be expressed pictorially as shown
below.
• The reactants can be elements or compounds, but the product
is always a compound.
The combination reaction between liquid
hydrogen and liquid oxygen propelled space
shuttles into orbit.
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2H2(ℓ) + O2(ℓ) → 2H2O(g)
UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.1
Decomposition Reactions
• A decomposition reaction is a chemical reaction in which a
single compound breaks down into two or more products.
• A decomposition reaction can be expressed pictorially as
shown below.
• The products may be a combination of elements and
compounds, but the reactant is always a compound.
In hydrolysis, energy is used to decompose
water into hydrogen gas and oxygen gas.
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2H2O(ℓ) → 2H2(g) + O2(g)
UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.1
Reviewing Combination and
Decomposition Reactions
What are the seven diatomic molecules that you need to know
when writing chemical equations for combination reactions?
In the electrolysis of water, what is the purpose of the battery
and what are the products of the reaction?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.1
Single Replacement Reactions
• A single replacement reaction is a chemical reaction in
which one element takes the place of another element in a
compound.
• A single replacement reaction can be expressed pictorially as
shown below.
Chlorine gas in the flask on the left bubbles through an
aqueous solution of sodium bromide. In a single
replacement reaction, the chlorine replaces the bromine
in the sodium compound.
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2NaBr(aq) + Cl2(g) → 2NaCl(aq) + Br2(ℓ)
UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.1
Double Replacement Reactions
• A double replacement reaction is a chemical reaction in
which the positive ions of two different compounds exchange
places, resulting in the formation of two new compounds.
• A double replacement reaction can be expressed pictorially as
shown below.
A red precipitate, Ag2CrO4(s), forms when
two ionic solutions, AgNO3(aq) and
K2CrO4(aq), undergo a double replacement
reaction.
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.1
Reviewing Single and Double
Replacement Reactions
Do metals or non-metals undergo single replacement
reactions?
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Why would it be more efficient for double replacement
reactions to occur in aqueous solution rather than the
reaction occurring between two solid compounds?
UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.1
Combustion Reactions
• A combustion reaction is a chemical reaction in which a
compound or element reacts with oxygen to form compounds
called oxides.
• The general equation of a combustion reaction is
CxHy + O2  CO2 + H2O
• Heat and light are often produced in a combustion reaction.
• What are two examples of combustion reactions?
• What is incomplete combustion, and why is it hazardous
when it occurs in homes?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Summary of Reaction Types
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Section 4.1
UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.1
Section 4.1 Review
• Chemical reactions can be classified as combination,
decomposition, single replacement, double replacement, or
combustion reactions.
• Combustion reactions may be complete or incomplete.
Incomplete combustion of organic compounds such as
hydrocarbons produces the toxic compound carbon monoxide.
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
4.2 Acids and Bases
• Some compounds are classified as an acid or a base.
• Citrus fruits, vinegar, soaps, and baking soda are examples of
acids and bases.
• What does this whip scorpion have to do with acids and bases?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
Acids
• An acid is a chemical that produces hydrogen ions when
dissolved in water. An acidic solution has a pH of less than 7.
• Acids taste sour. Many acids are corrosive, and they will react
with many substances.
How are
hydrofluoric
acid and this
glass globe
related?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
Bases
• A base is a chemical that produces hydroxide ions when
dissolved in water. A basic solution has a pH greater than 7.
• Bases taste bitter, and they have a slippery feel. Many bases
are corrosive, and they are often used in cleaning products.
Consumer products such as
cleaners often contain bases.
Which two elements make up a hydroxide ion?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
The pH Scale
• The pH scale is a numerical scale that is used for identifying a
solution as acidic, basic, or neutral.
• Acid solutions have a pH of less than 7. The lower the pH
number, the higher the concentration of hydrogen ions.
• Basic solutions have a pH of greater than 7. The higher the pH
number, the greater the concentration of hydroxide ions.
• A neutral solution has a pH of 7 and approximately the same
number of hydrogen ions and hydroxide ions.
Is a tomato that has a pH of about 4 acidic or basic?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
The pH Scale
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Section 4.2
UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
Differences in pH Values
• The concentration of hydrogen ions associated with a value on
the pH scale differs from the value above it or below it by a
power of 10.
• A solution that has a pH of 4 has a concentration of hydrogen
ions that is 10 times greater than a solution that is pH 5.
• The pH of a solution can be measured using pH paper or a pH
meter.
• If grapes have a pH of 3 and a banana has a pH of 5, how
much greater is the concentration of hydrogen ions in grapes
than in the banana?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
Identifying Acids and Bases
• An acid-base indicator is a chemical that has a characteristic
colour when in the presence of an acid or a base.
• Red and blue litmus papers can be used to determine if a
solution is an acid or a base. Red litmus paper turns blue in a
basic solution, and blue litmus paper turns red in an acidic
solution.
The pH paper on the left
and the pH meter on the
right both determine the pH
of a solution.
Are the solutions that were tested acidic or basic?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
A Summary of Acid and Base Properties
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
Names of Acids
• Two categories of acids are binary acids and oxoacids.
• Binary acids are composed of two elements—hydrogen and a
non-metal.
• Oxoacids are composed of hydrogen, oxygen, and another
element.
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HF(aq)
H2SO4(aq)
hydrofluoric acid
sulfuric acid
What are the rules for naming a binary acid and an
oxoacid using the classical method?
UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
Chemical Formulas of Acids
• The chemical formula of an acid can be considered composed
of a certain number of hydrogen ions and the negative ion.
• The negative ion is identified by the name of the acid.
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
Names and Chemical Formulas of Bases
• Bases are ionic compounds composed of metal ions and
hydroxide ions. Their names are written following the IUPAC
guidelines for ionic compounds.
• The chemical formula for a base includes enough hydroxide
ions in the formula to make the total charge of the compound
zero.
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
Acids in the Atmosphere and Waterways
• Rainwater is naturally acidic and normally has a pH of
between 5.6 to 5.8.
• Various human activities release compounds into the air that
lower the pH of precipitation.
What human
activities add
to acid
precipitation?
Why is acid
precipitation a
problem?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
Neutralization Reactions
• Neutralization is a chemical reaction between an acid and a
base that results in production of a salt and water.
• A salt, such as sodium chloride, is an ionic compound.
• The increased pH of waterways due to acid precipitation can
be temporarily reduced by adding calcium carbonate (lime) to
the water.
Why is liming
waterways a temporary
solution to the problem of
the effects of acid
precipitation?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
Salts Formed From Neutralization Reactions
• Different salts formed in the neutralization reactions between
acids and bases have a variety of uses.
• Commercially important salts include sodium chloride,
magnesium acetate, and calcium acetate.
What might
be the original
source of the
underground
salt deposits in
Canada?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
Section 4.2 Review
• Acids and bases are two important classes of compounds with
their own characteristic properties.
• The pH scale tells you how acidic or basic a substance is.
Acids have pH values below 7. Bases have pH values above
7. Neutral solutions have a pH of 7.
• Universal indicator, pH paper, and a pH meter are all tools for
determining the pH of a solution.
• Acids have both IUPAC and classical names. There are
special rules for naming binary acids and oxoacids.
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Continued…
UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.2
Section 4.2 Review
(continued)
• Bases are named using IUPAC guidelines for ionic
compounds.
• Rainwater is naturally acidic, but human activities can lower
the pH of rainwater further. This is called acid precipitation,
and it can severely damage ecosystems.
• When most acids and bases react, they form a salt and water.
The reaction between an acid and a base is called
neutralization.
• Antacids and the liming of lakes are examples of applications
of neutralization reactions.
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.3
4.3 Rates of Chemical Reactions
• Reaction rate is a measure of how fast a reaction occurs.
• Some reactions, such as the process of rusting, occur slowly
and some reactions, such as the deployment of air bags, occur
quickly.
Is the reaction
shown in this
photo occurring
slowly or quickly?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.3
Factors That Affect the Rate of a Reaction
There are four main factors that affect reaction rates.
• Higher temperatures result in an increase in frequency and
energy of collisions among particles.
• Increased surface area results in more collisions that result in
a reaction.
Glow sticks are powered by a
chemical reaction. Why might the
glow stick on the left be brighter?
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Continued…
UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.3
Factors That Affect the Rate of a Reaction
• A greater concentration of particles increases the chances that
a collision will result and a reaction will occur.
• Catalysts lower the energy required for a reaction to occur.
How could you increase
the reaction rate between the
wood and oxygen in the air?
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UNIT 2
Chapter 4: Classifying Compounds and Chemical Reactions
Section 4.3
Section 4.3 Review
• Chemical reactions occur at different rates. For example,
rusting is a slow reaction. The combustion of propane is a fast
reaction.
• Rates of reaction are affected by a number of factors,
including temperature, surface area, concentration, and the
presence of a catalyst.
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