Chapter 10
Chemical Reactions
Chemical Reactions
The process by which atoms of one or more
substances are rearranged to form different
substances is called a chemical reaction.
 Some ways to know that a chemical reaction has
occurred include absorption of heat and release
of energy in the form of light or heat, color
change, production of a gas, and the
appearance of gas bubbles or a solid.

Chemical Equations
Statements called equations are used to
represent chemical reactions.
 Reactants, or starting substances, and
the products, or substances formed
during a reaction, are shown in a chemical
reaction.
 The arrow in the reaction means “yields”.
 Plus signs separate different reactants and
products.

Examples
REACTANT + REACTANT
“yields”
PRODUCT + PRODUCT
State Symbols

Sometimes state symbols will be used to
indicate the state of matter in the
reaction.
– (s) Solid
– (l) Liquid
– (g) Gas
– (aq) Aqueous [Water solution]
Equations
Equations can be written in words, in
which the reactants and products are
indicated by their names.
 Word equations can be replaced by
skeleton equations which use chemical
formulas rather than words.
 Skeleton equations are more informative
because they identify the atoms that make
up each reactant and product.

Example

Write a word equation and skeleton
equation for the reaction in which
hydrogen gas reacts with oxygen gas to
form liquid water.
hydrogen(g) + Oxygen(g)
 H2 (g) + O2 (g)

Water (l)
H2O (l)
Practice

Write a word equation and a skeleton
equation for each of the following
descriptions of chemical reactions.
– Solid lithium reacts with chlorine gas to
produce solid lithium chloride.
– Nitrogen gas reacts with oxygen gas to
produce nitrogen dioxide gas.
– Solid iron reacts with aqueous copper (II)
nitrate to produce solid copper and aqueous
iron (II) nitrate.
Balanced Chemical Equations
Skeleton equations do not reflect the fact that
matter is conserved during a reaction.
 An equation must reflect that the same number
of each kind of atom on both sides of the arrow.
This is called a balanced chemical equation.
 To balance a chemical equation, use
coefficients, numbers placed in front of the
compound. When no coefficient appears, the
number is understood to be 1.

Procedure
1.
2.
3.
4.
5.
6.
Write the skeleton equation.
Count the atoms of the elements in the
reactants. Polyatomic atoms that remain
unchanged can be counted as elements.
Count the atoms of the elements in the
products.
Change coefficients to make numbers equal.
DO NOT CHANGE SUBSCRIPTS.
Write coefficients in their lowest possible
ratios.
Check your work.
Classifying Chemical
Reactions
Types of Reactions
There are five basic types of chemical
reactions.
 The first of these types is the Synthesis
reaction.
 In the synthesis reaction, there are more
than one reactants and only one product.
Synthesis means combine.

Combustion Reactions
A combustion reaction is a reaction that has
as one reactant oxygen gas.
 Combustion reactions produce lots of heat
and light and the product is usually carbon
dioxide and water.

CH4 (g)+ 2O2 (g)
CO2 (g) + 2H2O (g)
Decomposition

A decomposition reaction is one where a
single compound breaks down into two or
more elements or new compounds.
2Al2O3
4 Al + 3O2
Single-Replacement Reactions
In a single-replacement reaction, atoms of
an element replace the atoms of another
element in a compound.
 For example, in the replacement of silver
in silver nitrate by zinc metal.

Zn (s) + 2AgNO3 (aq)
Zn(NO3)2 (aq) + 2 Ag (s)
Activity Series
Not all metals will replace one another.
Only a metal that is more chemically
reactive will replace one that is less
reactive.
 The order of such reactivity is called an
activity series and you have a copy of one
in your reference tables.

Reactivity
Any metal in an activity series will replace
the metals below it in their compounds.
 With elemental halogens, one replaces the
other if the second lies below it in the
periodic table.
 Fluorine is more reactive than, chlorine,
which is more active than bromine, which
is more active than iodine.

Example
Use an activity series to predict the singlereplacement reaction that will occur
between aluminum metal and lead (II)
nitrate (Pb(NO3)2) in a water solution and
write its balanced chemical equation.
Answer:

2Al (s) + 3Pb(NO3)2 (aq)
2Al(NO3)3 (aq) + 3 Pb(s)
Practice

1.
2.
3.
4.
Predict whether a single-replacement reaction
will occur between the following pairs of
possible reactants. If so, write the balanced
chemical equation for the reaction.
Chlorine gas and aqueous potassium iodide
Magnesium metal and aqueous copper (II)
sulfate
Copper metal and iron (III) chloride in water
solution
Lead metal and aqueous silver nitrate
Double Replacement Reactions
In this reaction type, there is an exchange of the
positive ions between two compounds, often in
water solutions.
 Often a solid, of low solubility is produced during
the reaction and settles out of the solution. This
solid is called a precipitate.
 For example,

Pb(NO3)2 (aq) + 2NaCl (aq)
2NaNO3 (aq) +PbCl2 (s)
Practice

1.
2.
3.
Write a balanced chemical equation for each of the
following double-replacement reactions.
A water solution of sinc bromide (ZnBr2) and a water
solution of potassium hydroxide form a water solution
of potassium bromide and a precipitate of zinc
hydroxide.
A water solution of copper (II) sulfate and a water
solution of barium chloride produce a water solution of
copper (II) chloride and solid barium sulfate.
A precipitate of iron (III) carbonate and a water
solution of sodium nitrate are formed when a water
solution of iron (III) nitrate and a water solution of
sodium carbonate are mixed.
Reactions in Aqueous
Solutions
Solutions
When a substance dissolves in water, a
solution forms.
 A solution is a homogeneous mixture
because it has a constant composition
throughout.
 A solution contains one or more
substances called solutes dissolved in the
solvent.

Solutions (cont’d)
The solvent is the most plentiful
substance in the solution.
 An aqueous solution is a solution in
which the solvent is water.
 When dissolved to form aqueous
solutions, the ions of ionic compounds
separate.

Ionic Equations
To show all of the particles in solution as
they really exist, a complete ionic
equation can be written.
Na+ (aq) + Cl- (aq) + Ag+ (aq) + NO3- (aq)
Na+ (aq)+ NO3- (aq) + AgCl (s)
 Notice that the sodium and nitrate ions
are present on both sides of the equation.
Such ions that do not participate in the
reaction are called spectator ions.

Net Ionic Equations

An ionic equation that does not show
spectator ions but only the particles that
participate in the reaction is called a net
ionic equation.
Example

Write the balanced chemical equation for
the reaction between aqueous solutions of
strontium nitrate and potassium sulfate,
which forms the precipitate strontium
sulfate. Then write the complete ionic and
net ionic equations.
Practice

1.
2.
Write the balanced chemical, complete
ionic and net ionic equations for each of
the following reactions.
Aqueous solutions of lead (II) nitrate and
ammonium chloride are mixed, forming a
precipitate of lead (II) chloride.
Aqueous solutions of aluminum chloride
and sodium carbonate are combined,
producing solid aluminum carbonate.
Production of Water or a Gas
Some double-displacement reactions in
aqueous solution produce water or a gas
(or both) rather than a precipitate.
 When this happens, show the water or gas
as a product in the net ionic equation. DO
NOT IONIZE!!!

Example

When hydrochloric acid and potassium
hydroxide solutions are mixed, water
results, together with an aqueous solution
of potassium chloride. Write the balanced
chemical equation, a complete ionic
equation and a net ionic equation for this
reaction.
Practice

1.
2.
3.
Write the balanced chemical, complete ionic
and net ionic equations for the reactions
between the following substances, which
produce water.
Nitric acid (HNO3) and aqueous barium
hydroxide
Sulfuric acid (H2SO4) and aqueous sodium
hydroxide
Phosphoric acid (H3PO4) and aqueous lithium
hydroxide
Lab Tomorrow