Download Chemical change is a process that involves recombining atoms and

Chemical change is a process that involves recombining
atoms and energy flows.
In this unit, you will learn about...

General Outcome #3 – Identify and classify
chemical changes, and write word and
balanced chemical equations for significant
chemical reactions, as applications of
Lavoisier’s law for conservation of mass
○ Describe the evidence for chemical changes (energy
change, formation of gas or precipitate, color or
odour change, change in temperature)
○ Differentiate between endothermic and exothermic
chemical reactions
○ Translate word equations to balanced chemical equations
○
○
○
○
○
○
and vice versa for chemical reactions that occur in living and
non living systems
Classify and identify categories of chemical reactions
(formation, decomposition, hydrocarbon combustion, single
replacement, double replacement)
Predict the products of formation (synthesis) and
decomposition, single and double replacement and
hydrocarbon combustion chemical reactions, when given the
reactants
Interpret balanced chemical equations in terms of moles of
chemical species and relate the mole concept to the law of
conservation of mass
Identify chemical reactions that are significant in societies
Define the mole as the amount of an element containing 6.02
X 1023 atoms (Avogadro’s number) and apply the concept to
calculate quantifies of substances of other chemical species
Provide examples of household, commercial and industrial
processes that use chemical reactions to produce useful
substances and energy
The Ultimate Chemical Reaction

What do you think would be one of the
coolest things to experience??
3.1: Recognizing and Describing Chemical Reactions
In this section, you will learn
about...

General Outcome #3 – Identify and classify
chemical changes, and write word and
balanced chemical equations for significant
chemical reactions, as applications of
Lavoisier’s law for conservation of mass
○ Describe the evidence for chemical changes (energy
change, formation of gas or precipitate, color or odour
change, change in temperature)
○ Differentiate between endothermic and exothermic
chemical reactions
○ Identify chemical reactions that are significant in
societies
○ Provide examples of household, commercial and
industrial processes that use chemical reactions to
produce useful substances and energy
Did you know??

Slicing an onion causes your eyes to
sting because of a chemical reaction.
Slicing ruptures the onion’s cells
allowing substances to mix. A gas is
produced and reacts with the water in
your eyes – producing dilute sulfuric
acid!
Solubility and Reactions

Page 88
Practice 1-4 page 90
Important Examples of
Chemical Change

When was the last time you watched an
awesome display of fireworks? Fireworks is
one example of chemical change (occurs
when a substance or substances react in a
chemical reaction to create a different
substance or substances) occurring. Other
examples of chemical change include
dough rising, the changing taste of food
cooking on a barbecue, the combustion of
fuel in a motor vehicle, a glowing glow
stick, and the changing temperature of a
hot or cold pack.
Important Examples of
Chemical Change
The substances that react are called
reactants and the new substances that
are produced are called products
 The products have completely different
properties than the reactants

Energy Flow through Systems
1.
Which of these processes involve a
release of energy?
○
2.
Fireworks (a) and the glow stick (d) involve a
release of energy. Fireworks release heat, light,
and sound energy. The glow stick releases light
energy.
Which involve the absorption of energy?
○
The boiling water (b) and the baking (c) involve
the absorption of energy. Both absorb heat
energy produced by a gas flame or an electric
current passing through an element.
Energy Flow through Systems
3.
Which are chemical changes?
○ Chemical change involves a change to the
composition of the substance. Therefore,
chemical changes occur in (a), (c), and (d).
4.
Which are physical changes?
○ Physical change involves a change of state
(e.g., liquid to gas). A physical change occurs
in (b).
Reactions That Form Gases
Recall: evidence of chemical reactions
include the formation of gases and
precipitates.
 Familiar examples of chemical reactions
that result in the formation of gases are
breads and cakes rising and the inflation
of an automobile air bag.

Reactions That Form Solids

Some reactions form a solid that
hardens over a short period of time.
Epoxy glue is one example.
Showing States in Chemical
Formulas
Recall: (s), (l), (g), (aq) are the
subscripts that refer to the substances
state at room temperature. It is
important to always give as much
information as possible about a reaction.
 The following are guidelines for the
states of substances at room
temperature

Showing States in Chemical
Formulas

Elements
 Metals are solid, except mercury, which is a
liquid
 Most of the diatomic elements are gases
H2(g), N2(g), O2(g), F2(g) and Cl2(g). Bromine is
a liquid and iodine is a solid: Br2(l) and I2(s)
 Sulfur, phosphorus and carbon are solids
Showing States in Chemical
Formulas

Compounds
 All ionic compounds are solid at room
temperature
 An ionic compound that is very soluble is shown
as aqueous when it is dissolved in water. An
ionic compound that is slightly soluble is usually
shown as solid, even when it’s in water.
 Molecular compounds are very difficult to
predict. The smaller the molecules are, the
more they tend to be gases. The larger they
are, the more they tend to be liquids and solids.
For example, CH4(g) is a gas (natural gas),
C6H14(l) is a liquid component of gasoline and
C18H38(s) is bees wax.
Energy Changes

Energy flow is an essential part of any
chemical reaction, sometimes energy is
absorbed and other times energy is
released.
Exothermic Reactions

THE AUTOMOTIVE BATTERY
A lead-acid storage battery is an electrochemical device
that produces voltage and delivers electrical current. The
battery is the primary "source" of electrical energy used in
vehicles today. It's important to remember that a battery
does not store electricity, but rather it stores a series of
chemicals, and through a chemical process electricity is
produced. Basically, two different types of lead in an acid
mixture react to produce an electrical pressure called
voltage. This electrochemical reaction changes chemical
energy to electrical energy and is the basis for all
automotive batteries.

Exothermic reactions – chemical reaction that release
energy usually in the form of heat, light or electricity
Exothermic Reactions
Another important exothermic reaction is
the combustion of fossil fuels: coal, oil
and natural gas
 Combustion – chemical reaction that
occurs when oxygen reacts rapidly with
a substance to form a new substance
and gives off energy (also called
“burning”)

Exothermic Reactions
For example, coal is used to produce
electricity, the heat released by coal
combustion is used to make steam,
which drives turbines that produce
electricity.
 This process produces carbon dioxide,
which is a greenhouse gas that
contributes to climate change

coal
+ oxygen
carbon dioxide + energy
Endothermic Reactions
Endothermic reaction – chemical reaction
that absorbs energy
 For example, in a cold pack, it contains
chemicals that absorb energy directly from
the environment. When you squeeze the
package, you break a container inside the
pack that keeps the chemicals separate
from each other. When they mix and react,
they absorb energy and the whole mixture
cools down

Biochemical Reactions

Two examples of chemical reactions
important to life on Earth are
photosynthesis and respiration. These
two biochemical reactions (may be
endothermic or exothermic) form the
basis of life as almost all food produced
on Earth begins with photosynthesis.
Characteristics of Chemical
Reactions

Recall: All chemical reactions have
these characteristics
 All reactions involve the production of new
substances with their own characteristics
(state at room temperature, melting point,
colour and density)
 All reactions involve the flow of energy. This
may be detected by a change in
temperature during the reaction.
Endothermic reactions absorb energy and
exothermic reactions release energy.
Characteristics of Chemical
Reactions
 When new substances form in chemical
reactions, sometimes changes of state can
be observed. For example, the formation of
a gas (bubbles) or a solid (precipitate)
 All chemical reactions are consistent with
the law of conservation of mass
Any ideas as to what this means?
Conservation of Mass

In 1789, a French chemist, Antoine
Lavoisier, came to a very important
conclusion. Before we discuss this, try
to explain this;
○ Suppose 23.0g of magnesium metal is burned
in pure oxygen. When all of the white powder
is carefully collected and placed on a scale, its
mass is 39.0g. How can it weigh 16g more??
How does this make sense??
Conservation of Mass

First, let’s look at Lavoisier’s work. He stated that:
when a system of chemicals reacts completely, the
total mass of all of the reactants equals the total
mass of the products. In other words, in chemical
processes, the most important property to be
conserved is the number of atoms of each kind that
are present. Unlike nuclear processes, chemical
reactions do not create or destroy atoms, or change
one kind of atom into another. They only reshuffle the
atoms that were originally present into different
molecular combinations. What we would like to be
able to do is to count each kind of atom before and
after a reaction and make sure that none has been
gained or lost.
Conservation of Mass
Is Lavoisier’s conclusion wrong??
No, it’s not wrong, it’s actually telling us
that 16g of oxygen reacted with the 23g of
magnesium metal. The difference in mass
means that there is a reactant that we can’t
see – some new form of matter. The
difference of mass between the
magnesium and white powder product also
gives us the mass of this unseen
compound.
 His conclusion is called the law of
conservation of mass


3.2: Writing Chemical Equations
In this section you will learn
about...

General Outcome #3 – Identify and
classify chemical changes, and write
word and balanced chemical equations
for significant chemical reactions, as
applications of Lavoisier’s law for
conservation of mass
○ Translate word equations to balanced
chemical equations and vice versa for
chemical reactions that occur in living and non
living systems
Writing Chemical Equations

Chemical change involves chemical
reactions. To record what occurs in a
chemical reaction, chemists use a
balanced chemical equation made up of
chemical formulas.
Symbolizing Chemical Change

To write a chemical equation, you need
to know what substances react (the
reactants) and what new substances
form (the products). This requires you
to;
○ careful observations
○ knowledge of what substances are present at
the start of the reaction
○ the ability to analyze the materials produced
by the reaction
Symbolizing Chemical Change

Recall: chemical change is often
accompanied by visible events such as;
○ change in color
○ production of gas (bubbles)
○ release of heat (increased temperature)
○ appearance of a substance that is only slightly
soluble (cloudiness)
Writing Word Equations

Consider the chemical reaction between
a piece of magnesium metal with
hydrochloric acid. We can describe the
reaction with the following sentence;
 solid magnesium metal reacts with aqueous
hydrochloric acid to produce aqueous
magnesium chloride and hydrogen gas.
○ Which are the products? Which are the
reactants?
Writing Word Equations
The word equation for this reaction is;
magnesium + hydrochloric acid
magnesium chloride + hydrogen gas


The “+” sign groups the reactants and
the arrow separates the reactants from
the products (which is read “produces”),
then the products are separated by a “+”
sign as well
Writing Word Equations

Another example;
 An iron nail is placed in a solution of copper
(II) chloride
iron + copper (II) chloride
iron (II)
chloride + copper
Don’t worry about not knowing the products of
a chemical reaction, we’ll go through those
more in depth later!
Writing Balanced Formula
Equations
Formula equation – a chemical
equation that uses the reactants and
products in a chemical reaction
 Because mass is conserved in a
chemical reaction, you need to write a
balanced formula equation (a formula
equation that has the same number of
atoms of each element in both the
reactants and products)

Writing Balanced Formula
Equations
Let’s look at the formula for water;
hydrogen + oxygen
water
H2 (g) + O2 (g)
H2O(l)

This is called a skeleton equation
because it identifies the substances
involved in the reaction but it is not
balanced.
Writing Balanced Formula
Equations

How do you know the correct proportions?
 Recall: the law of conservation of mass – the
mass of the reactants must equal the mass of
the products
H2 (g) + O2 (g) → H2O(l)
 Follow these steps:
 Count the number of oxygen and balance
H2 (g) + O2 (g) → 2 H2O(l)
 Count the number of hydrogen and balance
2 H2 (g) + O2 (g) → 2 H2O(l)
Writing Balanced Formula
Equations

Try the following
N2 (g) + H2(g) → NH3(g)
 Count the number of nitrogen and balance
N2 (g) + H2(g) → 2NH3(g)
 Count the number of hydrogen and balance
N2 (g) + 3H2(g) → 2NH3(g)
Writing Balanced Formula
Equations

There is no specific element to try to
balance first, if you’re having trouble with
one element and it won’t seem to balance
then start with one of the other elements
first!
Writing Balanced Formula
Equations

Try to balance the following:
O2 (g) + CH4(g) → CO2(g) + H2O(g)
a.

2O2 (g) + CH4(g) → CO2(g) + 2H2O(g)
Fe(NO3)2(aq) + Na3PO4(aq) → NaNO3(aq) + Fe3(PO4)2(s)
b.

3Fe(NO3)2(aq) + 2Na3PO4(aq) → 6NaNO3(aq) + Fe3(PO4)2(s)
Practice 5-8 pg. 101
3.3: Five Common Types of Chemical Reactions
In this section, you will learn
about...

General Outcome #3 – Identify and classify
chemical changes, and write word and
balanced chemical equations for significant
chemical reactions, as applications of
Lavoisier’s law for conservation of mass
○ Classify and identify categories of chemical
reactions (formation, decomposition, hydrocarbon
combustion, single replacement, double
replacement)
○ Predict the products of formation (synthesis) and
decomposition, single and double replacement
and hydrocarbon combustion chemical reactions,
when given the reactants
Five Common Types of Chemical
Reactions
Chemists have looked at many different
types of reactions and found some
common characteristics. From the vast
array of reactions, a few types have
emerged and have also allowed us to
predict the outcome of many chemical
reactions by examining the reactants.
 The five common types of chemical
reactions are formation, decomposition,
hydrocarbon combustion, single
replacement and double replacement

Formation Reactions
reaction – two
elements combine to form a
compound (also known as
composition or synthesis)
 element + element = compound
OR
 A + B = AB
 Formation
Formation Reactions

Example:
 Word Equation:
○ sulfur + oxygen
sulfur dioxide
 Skeleton Equation:
○ S8(s) + O2(g)
SO2(g)
 Balanced Equation:
○ 1S8(s) + 8O2(g)
8SO2(g)
Formation Reactions

On your own, try
 Write the skeleton equation and balanced
equation for the following
○ formation of lithium oxide from its elements.
○ formation of lead (IV) bromide from its
elements.
○ formation magnesium oxide
○ Formation of iron (III) chloride
Formation Reactions

Skeleton Equation:
 Li(s) + O2(g)

Balanced Equation:
 4Li(s) + 1O2(g)

2Li2O(s)
Skeleton Equation:
 Pb(s) + Br2(g)

Li2O(s)
PbBr2(s)
Balanced Equation:
 Pb(s) + 2Br2(g)
PbBr4(s)
Formation Reactions

Skeleton Equation:
 Mg(s) + O2(g)

MgO(s)
Balanced Equation:
 2Mg(s) + 1O2(g)

Skeleton Equation:
 Fe(s) + Cl2(g)

2MgO(s)
FeCl3(s)
Balanced Equation:
 2Fe(s) + 3Cl2(g)
2FeCl3(s)
Decomposition Reactions
reaction –
products that can be broken
down into its reactants
 compound = element + element
OR
 AB = A + B
 Decomposition
Decomposition Reactions

Example:
 Word Equation:
○ aluminum chloride
aluminum + chlorine
 Skeleton Equation:
○ AlCl3(s)
Al(s) + Cl2(g)
 Balanced Equation:
○ 2AlCl3(s)
2Al(s) + 3Cl2(g)
Decomposition Reactions

On your own, try
 Write the balanced equation for the following
○ solid magnesium sulfide produces solid
magnesium and solid sulfur
○ solid potassium iodide produces solid
potassium and solid iodine
○ solid aluminum oxide produces solid
aluminum and oxygen gas
○ solid nickel (II) chloride produces solid nickel
and chlorine gas
Decomposition Reactions

Balanced Equation:
 8 MgS(s)

Balanced Equation:
 2 KI(s)

2 K(s) + I2(s)
Balanced Equation:
 2 Al2O3(s)

8 Mg(s) + S8(s)
4 Al(s) + 3 O2(g)
Balanced Equation:
 NiCI2(s)
Ni(s) + Cl2(g)
Hydrocarbon Combustion
Reactions
 Hydrocarbon
Combustion
reaction – substances that
contain hydrogen and carbon
 CxHy + O2(g)
CO2(g) + H2O(g)
OR
 hydrocarbon + oxygen produces
carbon dioxide + water
Hydrocarbon Combustion
Reactions

Example:
 Word Equation:
○ methane + oxygen
carbon dioxide + water
 Skeleton Equation:
○ CH4(l) + O2(g)
CO2(g) + H2O(g)
 Balanced Equation:
○ CH4(l) + 2 O2(g)
CO2(g) + 2 H2O(g)
Hydrocarbon Combustion
Reactions

On your own,
 Complete and balance each equation
○ C2H6(g) + O2(g)
○ C3H8(g) + O2(g)
○ C 6 H14(g) + O2(g)
○ C6H6(l) + O2(g)
Hydrocarbon Combustion
Reactions

On your own,
 Complete and balance each equation
○ 2 C2H6(g) + 5 O2(g)
4 CO2(g) + 6 H2O (g)
○ C3H8(g) + 5 O2(g)
3 CO2(g) + 4 H2O (g)
○ 2 C6H14(l) + 19 O2(g)
12 CO2(g) + 14 H2O(g)
○ 2 C6H6(l) + 15 O2(g)
12 CO2(g) + 6 H2O (g)
Single Replacement
Reactions
Replacement reaction – a
reactive element reacts with an ionic
compound, after the reaction the
element ends up in a compound and
one of the elements in the reactant
ends up as an element
 A + BC = AC + B
 Single
Single Replacement Reactions

Example:
 Word Equation:
○ magnesium + silver nitrate
magnesium nitrate
 Skeleton Equation:
○ Mg(s) + AgNO3(aq)
 Balanced Equation:
○ Mg(s) + 2 AgNO3(aq)
silver +
Ag(s) + Mg(NO3)2 (aq)
2 Ag(s) + Mg(NO3)2(aq)
Single Replacement Reactions

On your own, try
 Write the balanced equation for the following
○ aluminum is added to copper (II) chloride, which
produces copper and aluminum chloride
○ bromine is mixed with iron (III) iodide to produce
iodine and iron (III) bromide
○ chlorine gas is added to a solution of aqueous
nickel (III) bromide and the mixture is stirred; it
produces aqueous nickel (III) chloride and liquid
bromine
○ zinc metal is placed into a solution of silver nitrate
and allowed to sit. This produces aqueous zinc
nitrate and solid silver metal
Single Replacement Reactions

Balanced Equation:
 2 Al(s) + 3 CuCl2(aq)

Balanced Equation:
 3 Br2(s) + 2 FeI3(aq)

3 I2(s) + 2 FeBr3(aq)
Balanced Equation:
 3 Cl2(g) + 2 NiBr3(aq)

3 Cu(s) + 2 AlCl3(aq)
3 Br2(s) + 2 ZnCl3(aq)
Balanced Equation:
 Zn(s) + 3 AgNO3(aq)
3 Ag(s) + Zn(NO3)3(aq)
Double Replacement
Reactions
Replacement reaction – the
ions in the first compound join with
ions in the second compound
 AB + CD = AD + BC
 Double
Double Replacement Reactions

Example:
 Word Equation:
○ lead (II) nitrate + sodium iodide
iodide + sodium nitrate
 Skeleton Equation:
○ Pb(NO3)2(aq) + NaI(aq)
 Balanced Equation:
○ Pb(NO3)2(aq) + 2 NaI(aq)
lead (II)
NaNO3(aq) + PbI2(aq)
2 NaNO3(aq) + PbI2(aq)
Double Replacement Reactions

On your own, try
 Write the balanced equation for the following
○ when aqueous copper (I) nitrate and aqueous
magnesium bromide are mixed, a precipitate of
solid copper (I) bromide forms along with aqueous
magnesium nitrate
○ when aqueous aluminum chloride and aqueous
sodium hydroxide are mixed, a precipitate of solid
aluminum hydroxide forms as well as aqueous
sodium chloride
Double Replacement Reactions

Balanced Equation:
○ 2 CuNO3(aq) + MgBr2 (aq)

Mg(NO3)2(aq) + 2 CuBr(s)
Balanced Equation:
○ 3 NaOH(aq) + AlCI3(aq)
Al(OH)3(s) + 3 NaCl(aq)
3.4: The Mole
In this section, you will learn
about...

General Outcome #3 – Identify and classify
chemical changes, and write word and
balanced chemical equations for significant
chemical reactions, as applications of
Lavoisier’s law for conservation of mass
○ Interpret balanced chemical equations in terms of
moles of chemical species and relate the mole
concept to the law of conservation of mass
○ Define the mole as the amount of an element
containing 6.02 X 1023 atoms (Avogadro’s number)
and apply the concept to calculate quantifies of
substances of other chemical species
Did you know??

Mole day is celebrated on October 23
each year. It begins at 6:02 am and
ends at 6:02 pm. The numbers are
associated with these dates and times
derived from Avogadro’s number, a
constant known to all chemists in the
world. It’s value is approximately
6.02 X 1023
The Mole
Chemists deal with atoms and
molecules all the time, and they need to
measure quantities of matter precisely.
Balanced equations indicated the
correct proportion of atoms and
molecules to use in a reaction.
 Since atoms and molecules are very
small, the quantity used to measure
them needs to be a very large number.

Molar Mass
Molar mass – the mass of one mole of
a substance
 Experiments have been done to
determine the atomic molar mass (found
on the periodic table), you can use the
atomic molar mass to find the molar
mass of any substance

Avogadro’s Number and the Mole
Mole – the quantity that chemists use to
measure elements and compounds
(symbol: mol)
 The number of particles in 1 mol is
called Avogadro’s number (6.02X1023)
 To define the mole, chemists chose to
work with an isotope of the element
carbon-12. Carbon is a stable solid, so
it is easy to work with.

Molar Mass

What is the molar mass of methane?
 formula: CH4 (g) – contains one carbon atom
and four hydrogen atoms
 H = 1.01 g/mol X 4 = 4.04 g/mol
 C = 12.01 g/mol X 1 = 12.01 g/mol
 Add them together to get 16.05 g/mol
Therefore the molar mass for one molecule of
methane is 16.05 g/mol.
Molar Mass

In other words, to find molar mass:
m=nXM
where
m is the quantity of matter in grams (g)
n is the quantity of matter in moles (mol)
M is the molar mass (g/mol)
The Factor-Label Method of
Converting between Quantities

This is used for converting between the
number of moles of a substance and its
mass.
 Because 1 mol C = 12.01g C their ratio has
a value of 1
 12.01g C = 1 The fraction is called a “factor”
1 mol C
and the units are called “labels”
 To find 3.000 moles of carbon: Since this is a
moles-to-mass conversion, we choose the factor
that has “mole” in the denominator so it will
cancel out the “mol” in 3.000 mol.
 mc= 3.00 mol X 12.01g
1 mol
The Factor-Label Method of
Converting between Quantities

mc= 3.00 mol X 12.01g = 36.03 g C
1 mol
Try the following
a. How many moles of silicon are in a 56.18 g
sample?
○
n = m = 56.18g = 2.000 mol
M 28.090 g/mol
b. What is the mass of 10.0 mol of water?
○
m=nXM
m = 10.0 mol X 18.02 g/mol
m = 180 g of water
The Mole Concepts and the Law
of Conservation of Mass
Recall: the law of conservation of mass
states that, in any reaction, the total mass
of the reactants equals the total mass of
the products.
 When chemists read equations that have
been balanced, they often read the
coefficients as moles. One reason is that
you can see a mole of something, while it
is impossible to see an atom of something.
Another reason is that chemists use the
mole to measure out chemicals.

The Mole Concepts and the Law
of Conservation of Mass

For example, consider the reaction of
sodium metal with oxygen gas
word: sodium + oxygen
sodium oxide
balanced: 4 Na(s) + O2(g)
2Na2O(s)
you can read it as:
4 atoms Na(s) + 1 molecule O2(g)
2 molecules Na2O(s)
it can also be read as:
4 moles Na(s) + 1 mole O2(g)
2 moles Na2O(s)
Did you know??
If you had Avogadro’s number of
toonies, or 1 mol of toonies, they
would cover all of Canada to a height
of about 60 km and all of Earth to a
height of about 1 km.