Science 1206
Unit 2: Chemistry
Chemical Reactions
Unit 2: Chemistry
Chemical Reactions
Chemical reactions are a part of our everyday life.
Brushing our teeth, getting a ride to school in the
family car, digesting food, and many others are all
examples of chemical reactions. The reactions may
be very complex, as in the creation of explosives, or
they may be very simple, as in the reaction of a
bathroom cleaner and a stain.
The basic structure of a chemical reaction is the
creation of some new substance(product) from the
reaction of one, two, or more, initial
substances(reactants).
Reactants
—> Products
2 Na + CaO
—> Na2O + Ca
Sodium reacts with calcium oxide to produce sodium
oxide and calcium
Types of Reactions
There are five basic types of chemical reactions.
These include.
1.
2.
3.
4.
5.
6.
Synthesis / Simple Composition Reactions
Decomposition / Simple Decomposition
Reactions
Double Replacement/Double Displacement
Single Replacement/Single Displacement
Combustion Reactions
Other
The Law of Conservation
of Mass
In a chemical reaction, the total mass of the reactants
is always equal to the total mass of products.
Mass(reactants) =
Mass(products)
Example 1:
NaCl +
12g
CaO —>
20g —>
Mass(reactants)
Mass(products)
=
=
Na2O +
15g
CaCl2
17g
12g + 20g =
15g + 17g =
32g
32g
Example 2:
NaCl +
18g
CaO —>
40g —>
Mass(reactants)
Mass(products)
=
=
Na2O +
30g
CaCl2
?g
18g + 40g =
20g + ?g =
58g
58g
Types of Chemical
Equations:
There are three basic representations of reaction
equations. These are;
Word Equations
a way of writing chemical reactions
in which the left side of the equation lists the names of
all the reactants and the right side of the equation lists
the names of all of the products. Let’s look at the
chemical reaction where iron reacts with oxygen to
produce iron(III) oxide(rust)
Example:
Iron + Oxygen —> Iron (III) oxide
Skeleton Equation a representation of a chemical
reaction in which formulas of the reactants are
connected to the formulas of the products by an
arrow.
Example:
Fe + O2 —> Fe2O3
Balanced Equation
an equation in which the
reactants and products contain equal number of
each type of atoms.
Example:
4 Fe + 3 O2 —> 2 Fe2O3
Four formula units of iron react with three molecules of
oxygen to produce two formula units of iron(III) oxide.
Example:
CH4 + 2O2 —> CO2 + 2 H2O
One molecule of methane reacts with two molecules
of oxygen to produce one molecule of carbon
dioxide and two molecules of water.
In a chemical reaction it is very important that the
numbers of individual atoms on one side of the
equation is equal to the number of individual atoms
on the other side of the reaction. In the above
reaction equation, for example, you will notice that
there are four iron atoms on both the reactant and
product sides of the equation.
Type 1:
Synthesis / Simple Composition Reactions
• to synthesize is to ‘create’
• when elements or compounds combine to form a
new substance a synthesis reaction occurs
• can be compared to the formation of a new
‘couple’ from two individuals
Model:
A + B —> AB
element + element —> compound
simple compound + simple compound —> complex
compound
Example1:Hydrogen and oxygen react to produce
water
word equation:
hydrogen + oxygen —> water
skeleton equation:
H2 + O2 —> H2O
balanced equation:
2 H2 + O2 —> 2 H2O
Example 2:Hydrochloric acid and ammonia react to
produce ammonium chloride
word equation:
Hydrochloric acid + ammonia —>
ammonium chloride
skeleton equation:
HCl + NH3 —> NH4Cl
balanced equation:
HCl + NH3 —> NH4Cl
same as skeleton equation
Example 3: Write word, skeleton and balanced
chemical equations for the synthesis of aluminum
chloride
word equation:
skeleton equation:
balanced equation:
Type 2:Decomposition / Simple Decomposition
Reactions
• to decompose is to ‘break down’
• when compounds break down into two or more
elements or compounds a decomposition reaction
occurs.
• can be compared to the ‘break-up’ of a couple
Model:
AB —> A + B
compound —> element + element
complex compound —> simple compound + simple
compound
Example 1: Nitrogen triodide decomposes to its
individual elements
word equation:
Nitrogen triodide —> nitrogen +
iodine
skeleton equation:
NI3 —> N2 + I2
balanced equation
2 NI3 —> N2 + 3 I2
Example 2:
Sodium chloride decomposes to its
individual elements
word equation:
Sodium chloride
chlorine
—>
sodium +
skeleton equation:
NaCl —>
Na + Cl2
balanced equation:
2 NaCl —> 2 Na + Cl2
Example 3: Write a word, skeleton and balanced
chemical equation for the decomposition of gallium
sulfide.
word equation:
skeleton equation:
balanced equation:
Type 3:
Single Replacement/Single Displacement
• when an element replaces another element in a
compound to form a new substance a single
replacement reaction occurs
• think of this kind of reaction as a person ‘cutting in’
on a couple dancing
Model:
AC + B —> A + BC
compound + element —> compound + element
Example1:
produce .......
Sodium reacts with calcium oxide to
word equation:
sodium + calcium oxide —> sodium
oxide + calcium
skeleton equation:
Na + CaO —> Na2O + Ca
balanced equation:
2Na + CaO —> Na2O + Ca
Example 2:Calcium iodide reacts with chlorine to
produce calcium chloride and iodine
word equation:
calcium iodide + chlorine —>
calcium chloride + iodine
balanced equation:
CaI2 + Cl2 —> I2 + CaCl2
Example 3: Demo
Copper reacts with silver nitrate to produce ..........
word equation:
Copper + silver nitrate —>
balanced equation:
Cu + AgNO3 —>
Example 4: Demo
Magnesium reacts with silver nitrate to produce.........
word equation:
magnesium + silver nitrate —>
balanced equation:
Mg + AgNO3 —>
Type 4:Double Replacement/Double Displacement
• when an element in one compound replaces an
element in a another compound to form two new
substances a double replacement reaction occurs
• think of this type of reaction as two couples
dancing and part ways through the dance they
switch partners
Model:
AC + BD —> AD + BC
compound + compound —> compound +
compound
Example 1: Sodium chloride reacts with calcium oxide
to produce .........
word equation:
sodium chloride + calcium oxide —>
sodium oxide + calcium chloride
skeleton equation: NaCl + CaO —> Na2O + CaCl2
balanced equation: 2 NaCl + CaO —> Na2O +
CaCl2
Example 2: Magnesium sulfide reacts with aluminum
oxide to produce .....
word equation:
magnesium sulfide + aluminum
oxide —>
balanced equation:
MgS + Al2O3 —>
Example 3: Gallium sulfate reacts with iron III nitrate to
produce ...
word equation:
Gallium sulfate + iron III nitrate —>
balanced equation:
Ga2(SO4)3 + Fe(NO3)3 —>
Example 4: Demo
Calcium carbonate reacts with hydrochloric acid to
produce calcium chloride, carbon dioxide and
hydrogen gas
word equation:
Calcium carbonate + hydrochloric
acid —> calcium chloride +
carbon dioxide + hydrogen
balanced equation
CaCO3 + HCl(aq) —> CaCl2
+ CO2 + H2
Neutralization
A neutralization reaction is a special case of a double
replacement reaction that involves the reaction of an
acid substance with a base substance to produce a
salt and water.
Model:
Acid + base —> salt + water
Example 5: Hydrochloric acid reacts with sodium
hydroxide to produce ...
word equation:
hydrochloric acid + sodium
hydroxide —>
balanced equation:
HCl + NaOH —>
Type 5:Hydrocarbon Combustion Reactions
• rapid reaction of a substance with oxygen to
produce an oxide
• fuel + oxygen —> oxides + energy
One of the most important current fuel sources on this
planet is hydrocarbons (Carbon and Hydrogen)
Model:
hydrocarbon + oxygen —> carbon dioxide + water
vapour
Example 1: Write a word and reaction equation for
the complete combustion of butane.
word equation:
butane + oxygen —> carbon
dioxide + water vapour
skeleton equation:
C4H10 + O2 —> CO2 + H2O
reaction equation:
2 C4H10 + 13 O2 —> 8 CO2 +
10 H2O
Example 2: Write a word and reaction equation for
the complete combustion of methane.
word equation:
methane + oxygen —> carbon
dioxide + water vapour
reaction equation:
CH4 + 2 O2 —> CO2 + 2 H2O
Example 3: Write a word and reaction equation for
the complete combustion of gasoline(C8H18) .
word equation:
gasoline + oxygen —> carbon
dioxide + water vapour
reaction equation:
C8H18 + 12.5O2 —> 8CO2 + 9H2O
2 C8H18 + 25 O2 —> 16 CO2 + 18 H2O
Example 4: Write a word and reaction equation for
the complete combustion of propane(C3H8).
word equation:
gasoline + oxygen —> carbon
dioxide + water vapour
reaction equation:
C3H8 + 5 O2 —> 3 CO2 + 4 H2O
Example 5: Write a word and reaction equation for
the complete combustion of cyclopropane(C3H6).
word equation:
cyclopropane + oxygen —>
carbon dioxide + water vapour
reaction equation:
2 C3H6 + 9 O2 —> 6 CO2 + 6 H2O
Incomplete Combustion
When materials burn and the conditions are not
perfect the combustion is incomplete. The materials
do not completely change and four products are
produced instead of two.
Model:
hydrocarbon + oxygen —> carbon monoxide + carbon
+ carbon dioxide + water vapour
2 C4H10 + 13 O2 —> 8 CO + 10 C + 8 CO2 + 10 H2O
Other
All reactions that do not fit into the categories above.
Evidence of Chemical
Reactions
1. Precipitate forms: New substance forms which has
a lower solubility than the original substance
2. Gas forms: A new substance is formed which is a
gas in the lab conditions of temperature and
pressure
3. Colour change: A new substance is formed which
has a different colour than the original substance
4. Energy Change: Heat produced or used. Energy is
released or absorbed to obey the Law of
Conservation of Energy
o Releases energy - Exothermic
o Absorbs Energy Endothermic
Phase of compounds and elements at room
Temperature
Denoted in subscripts at the end of an element or
compound name
(s)
solid
(l)
liquid
(g)
gas
(aq) aqueous - soluble in water
Determining Phase - in chemical equations
Elements - use periodic table
Molecular compounds - personal experience - see
table below
Ionic Compounds
• all ionic compounds not in water are solids
• when ionic compounds are placed in water some
completely dissociate, or completely dissolve (are
soluble), while other ionic compounds do not
Solubility of Ionic Compounds
• the solubility table on your periodic table is required
to determine the phase of ionic compounds in
water. When one of the reactants has an (aq) there
is water present and therefore you need to
determine the phase of the products.
• to use the table find the anion (the negative part of
the compound)
• example BaSO4 - look up the SO4 in the table. Most
are highly soluble but not Ba2+. So we would write
BaSO4 (s)
• example CuSO4 - look up the SO4 in the table. Most
are highly soluble and Cu2+ is not in the list of those
that have low solubility. So we would write CuSO4(aq)