Chapter #7
Chemical Reactions
CHAPTER #7 CONTENTS
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7-1 Grade School Volcanoes, Cars, & Detergents
7-2 Evidence of Chemical Reactions
7-3 The Chemical Equation
7-4 How to Write Balanced Chemical Equations
7-10 Classification of Chemical Reactions
7-9 Oxidation Reduction Reactions
7-5 Aqueous Solutions and Solubility
7-6 Precipitation Reactions
7-7 Aqueous Reactions
7-8 Acid/Base and Gas Evolution Reactions
7-2 Chemical Change Evidence
Chapter 6
7-2 Chemical Change Evidence
What is a clue that a chemical reaction has
occurred?
a)
b)
c)
d)
The color changes.
A solid forms.
Bubbles are present.
A flame is produced.
Chapter 6
7-2 Chemical Change Evidence
What is a clue that a chemical reaction has
occurred?
“Colorless hydrochloric acid is added to
a red solution of cobalt(II) nitrate, turning
the solution blue.”
a)
b)
c)
d)
The color changes.
A solid forms.
Bubbles are present.
A flame is produced.
Chapter 6
7-2 Chemical Change Evidence
What is a clue that a chemical reaction has
occurred?
“A solid forms when a solution of sodium
dichromate is added to a solution of lead
nitrate.”
a)
b)
c)
d)
A gas forms.
A solid forms.
Bubbles are present.
A flame is produced.
Chapter 6
7-10 Chemical Reactions
• A chemical equation is an abbreviated way to
show a chemical or physical change
• A chemical change alters the physical and
chemical properties of a substance
• Factors that indicate a chemical change
–
–
–
–
Change in color
Temperature change
Change in odor
Change in taste (we do not taste chemicals)
• Reactions always contain an arrow that
separates the reactants from the products
Reactants
Products
Chapter 6
7-10 Types of Chemical Reactions
•
Combination reaction (synthesis)
– Elements for reactants
– Examples:
H2 + O2
N2 + H2
Al + O2
H2O
NH3
Al2O3
The Law of Conservation of matter,
states matter cannot be created nor
destroyed, the means equations must be
balanced.
7-10 Types of Chemical Reactions
Balance the first equation
H2 + O2
H 2O
Note two oxygen atoms on the reactant side
and only one on the product side,
therefore place a two in front of water
7-10 Types of Chemical Reactions
Balance the first equation
H2 + O2
2H2O
Note two oxygen atoms on the reactant side
and only one on the product side,
therefore place a two in front of water
The two now doubles everything in water,
thus 4 hydrogen and 2 oxygen. Now place
a 2 in front of hydrogen.
7-10 Types of Chemical Reactions
Balance the first equation
2H2 + O2
2H2O
Note two oxygen atoms on the reactant side
and only one on the product side,
therefore place a two in front of water
The two now doubles everything in water,
thus 4 hydrogen and 2 oxygen. Now place
a 2 in front of hydrogen.
7-10 Types of Chemical Reactions
Now balance the second equation
N2 + H2
NH3
Note two nigrogen atoms on the reactant
side and only one on the product side.
Place a 2 in front of ammonia
7-10 Types of Chemical Reactions
Now balance the second equation
N2 + H2
2NH3
Note two nitrogen atoms on the reactant
side and only one on the product side.
Place a 2 in front of ammonia. This makes 2
nitrogen atoms and 6 hydrogen atoms.
Now place a 3 in front of hydrogen to
balance hydrogen atoms.
7-10 Types of Chemical Reactions
Now balance the second equation
N2 + 3 H2
2NH3
Note two nitrogen atoms on the reactant
side and only one on the product side.
Place a 2 in front of ammonia. This makes 2
nitrogen atoms and 6 hydrogen atoms.
Now place a 3 in front of hydrogen to
balance hydrogen atoms.
7-10 Types of Chemical Reactions
• Decomposition Reaction
– Compounds form simpler compounds or
elements.
– Examples
H2O
H2 + O2
7-10 Types of Chemical Reactions
• Decomposition Reaction
– Compounds form simpler compounds or
elements.
– Examples
2H2O
H2 + O2
7-10 Types of Chemical Reactions
• Decomposition Reaction
– Compounds form simpler compounds or
elements.
– Examples
2H2O
2H2 + O2
• Notice decomposition reactions are the
opposite of combination reactions
7-10 Types of Chemical Reactions
Single Replacement reactions have an
element and a compound for reactants.
Example:
Zn + HCl
How do we predict the products? Trade
places with the metal or nonmetal with the
metal or nonmetal in the compound
7-10 Types of Chemical Reactions
Single Replacement reactions have an
element and a compound for reactants.
Example:
Zn + HCl
How do we predict the products? Trade
places with the metal or nonmetal with the
metal or nonmetal in the compound
7-10 Types of Chemical Reactions
Single Replacement reactions have an
element and a compound for reactants.
Example:
Zn + HCl
ZnCl + H
Now make the products stable. Slide with
Clyde
7-10 Types of Chemical Reactions
Single Replacement reactions have an
element and a compound for reactants.
Example:
Zn + HCl
ZnCl2 + H2
Now make the products stable. Slide with
Clyde
7-10 Types of Chemical Reactions
Single Replacement reactions have an
element and a compound for reactants.
Example:
Zn + HCl
ZnCl2 + H2
Now make the products stable. Slide with
Clyde
Now Balance
7-10 Types of Chemical Reactions
Single Replacement reactions have an
element and a compound for reactants.
Example:
Zn + 2HCl
ZnCl2 + H2
Now make the products stable. Slide with
Clyde
Now Balance
7-10 Types of Chemical Reactions
Single Replacement reactions have an
element and a compound for reactants.
Another Example:
Cl2 + MgBr2
How do we predict the products? Trade
places with the metal or nonmetal with the
metal or nonmetal in the compound. In
this case we are trading nonmetals
7-10 Types of Chemical Reactions
Single Replacement reactions have an
element and a compound for reactants.
Another Example:
Cl2 + MgBr2
Br + MgCl
How do we predict the products? Trade
places with the metal or nonmetal with the
metal or nonmetal in the compound. In
this case we are trading nonmetals
7-10 Types of Chemical Reactions
Single Replacement reactions have an
element and a compound for reactants.
Another Example:
Cl2 + MgBr2
Br2 + MgCl2
How do we predict the products? Trade
places with the metal or nonmetal with the
metal or nonmetal in the compound. In
this case we are trading nonmetals
7-10 Types of Chemical Reactions
Double Replacement reactions contain
compounds as reactants.
HCl + Ca(OH)2
CaCl + HOH
Check formulas, and slide with Clyde when
necessary
7-10 Types of Chemical Reactions
Double Replacement reactions contain
compounds as reactants.
HCl + Ca(OH)2
CaCl2 + HOH
Check formulas, and slide with Clyde when
necessary
7-10 Types of Chemical Reactions
Double Replacement reactions contain
compounds as reactants.
2HCl + Ca(OH)2 CaCl2 + 2HOH
Check formulas, and slide with Clyde when
necessary
Now Balance!
7-10 Types of Chemical Reactions
Combustion Reactions occur when an element
or compound combine with oxygen to produce
oxides of each element.
H2 + O2
CH4 + O2
What is the oxide of hydrogen?
7-10 Types of Chemical Reactions
Combustion Reactions occur when an element
or compound combine with oxygen to produce
oxides of each element.
H2 + O2
CH4 + O2
What is the oxide of hydrogen? Water
7-10 Types of Chemical Reactions
Combustion Reactions occur when an element
or compound combine with oxygen to produce
oxides of each element.
H2 + O2
H2O
CH4 + O2
What is the oxide of hydrogen? Water
And the oxide of carbon?
7-10 Types of Chemical Reactions
Combustion Reactions occur when an element
or compound combine with oxygen to produce
oxides of each element.
H2 + O2
H2O
CH4 + O2
CO2 + H2O
What is the oxide of hydrogen? Water
And the oxide of carbon? Carbon dioxide
7-10 Types of Chemical Reactions
Combustion Reactions occur when an element
or compound combine with oxygen to produce
oxides of each element.
2H2 + O2
2H2O
CH4 + O2
CO2 + H2O
Now balance
7-10 Types of Chemical Reactions
Combustion Reactions occur when an element
or compound combine with oxygen to produce
oxides of each element.
2H2 + O2
2H2O
CH4 + O2
CO2 + 2H2O
Now balance
7-10 Types of Chemical Reactions
Combustion Reactions occur when an element
or compound combine with oxygen to produce
oxides of each element.
2H2 + O2
2H2O
CH4 + 2O2
CO2 + 2H2O
Now balance
7-10 Types of Chemical Reactions
REDOX reactions where the oxidation number
changes from reactants to products.
Oxidation is when the oxidation number
increases, by losing of electrons.
Reduction is when the oxidation number
decreases by gaining electrons.
Consider the following equation:
H2 + O2
H2 O
What are the oxidation numbers of hydrogen and
oxygen?
7-10 Types of Chemical Reactions
REDOX reactions where the oxidation number
changes from reactants to products.
Oxidation is when the oxidation number
increases, by losing of electrons.
Reduction is when the oxidation number
decreases by gaining electrons.
Consider the following equation:
0
0
H2 + O2
H2 O
What are the oxidation numbers of hydrogen and
oxygen?
7-9 REDOX REACTIONS
0
0
H2 + O2
2(1+) 2- = 0
H2O
How about hydrogen and oxygen in water?
7-9 REDOX REACTIONS
0
0
H2 + O2
oxidized
2(1+) 2- = 0
H2O
reduced
How about hydrogen and oxygen in water?
Oxidation is caused by the oxygen molecule,
so it is referred to as the oxidizing agent
(OA)
Reduction is caused by the hydrogen
molecule, so it is referred to as the
reducing agent (RA)
7-9 REDOX REACTIONS
Note:
• All of the previously discussed reactions
are REDOX except the double
replacement reactions.
• The number of electrons lost is equal to
the number of electrons gained in a
reaction. Why?
• Most elements have variable oxidation
numbers, except for hydrogen, oxygen,
and the memorized polyatomic ions.
7-9 REDOX REACTIONS
Oxidation numbers for a compound must
add up to equal zero, while the oxidation
numbers for a polyatomic ion must up to
equal the charge of that ion.
Consider the following chlorine compounds
1+
4(2-)=0
HClO4, HClO3, HClO2, HClO, Cl2, HCl
What is the oxidation number of chlorine in
each of these compounds, assuming
H+ and oxygen is 2-
7-9 REDOX REACTIONS
Oxidation numbers for a compound must
add up to equal zero, while the oxidation
numbers for a polyatomic ion must up to
equal the charge of that ion.
Consider the following chlorine compounds
1+ 7+ 4(2-)=0
HClO4, HClO3, HClO2, HClO, Cl2, HCl
What is the oxidation number of chlorine in
each of these compounds, assuming H is
1+ and oxygen is 2-
7-9 REDOX REACTIONS
Oxidation numbers for a compound must
add up to equal zero, while the oxidation
numbers for a polyatomic ion must up to
equal the charge of that ion.
Consider the following chlorine compounds
1+ 7+ 4(2-)=0
5+
HClO4, HClO3, HClO2, HClO, Cl2, HCl
What is the oxidation number of chlorine in
each of these compounds, assuming H is
1+ and oxygen is 2-
7-9 REDOX REACTIONS
Oxidation numbers for a compound must
add up to equal zero, while the oxidation
numbers for a polyatomic ion must up to
equal the charge of that ion.
Consider the following chlorine compounds
1+ 7+ 4(2-)=0
5+
3+
HClO4, HClO3, HClO2, HClO, Cl2, HCl
What is the oxidation number of chlorine in
each of these compounds, assuming H is
1+ and oxygen is 2-
7-9 REDOX REACTIONS
Oxidation numbers for a compound must
add up to equal zero, while the oxidation
numbers for a polyatomic ion must up to
equal the charge of that ion.
Consider the following chlorine compounds
1+ 7+ 4(2-)=0
5+
3+
1+
HClO4, HClO3, HClO2, HClO, Cl2, HCl
What is the oxidation number of chlorine in
each of these compounds, assuming H is
1+ and oxygen is 2-
7-9 REDOX REACTIONS
Oxidation numbers for a compound must
add up to equal zero, while the oxidation
numbers for a polyatomic ion must up to
equal the charge of that ion.
Consider the following chlorine compounds
1+ 7+ 4(2-)=0
5+
3+
1+
0
HClO4, HClO3, HClO2, HClO, Cl2, HCl
What is the oxidation number of chlorine in
each of these compounds, assuming H is
1+ and oxygen is 2-
7-9 REDOX REACTIONS
Oxidation numbers for a compound must
add up to equal zero, while the oxidation
numbers for a polyatomic ion must up to
equal the charge of that ion.
Consider the following chlorine compounds
1+ 7+ 4(2-)=0
5+
3+
1+
0
1HClO4, HClO3, HClO2, HClO, Cl2, HCl
What is the oxidation number of chlorine in
each of these compounds, assuming H is
1+ and oxygen is 2-
7-9 REDOX REACTIONS
3(2-)=2-
How about sulfur in SO3 2-
7-9 REDOX REACTIONS
4+ 3(2-)=2-
How about sulfur in SO3 212(1+)+6(2-)=0
How about carbon in C6H12O6
7-9 REDOX REACTIONS
4+ 3(2-)=2-
How about sulfur in SO3 20 + 12(1+)+6(2-)=0
How about carbon in C6H12O6
7-5 Aqueous Ionic Compounds
Most ionic compounds dissolve in water to
produce solutions that conduct electricity. The
degree to which a solution will conduct electricity is
used to determine if a solute is a strong or weak
electrolyte. Solutions that do not conduct
electricity are called nonelectrolytes. Molecular
compounds that dissolve in water to conduct
electricity, are acids or bases. Strong acids/bases
are referred to as strong electrolytes since they are
good conductors of electricity. Weak acid solutions
do not conduct electricity well and are called weak
electrolytes
7-5 Aqueous Ionic Compounds
Most ionic compounds dissolve in water to produce
solutions that conduct electricity. The degree to
which a solution will conduct electricity is used to
determine if a solute is a strong or weak electrolyte.
Solutions that do not conduct electricity are called
nonelectrolytes. Molecular compounds that dissolve
in water to conduct electricity, are acids or bases.
Strong acids/bases are referred to as strong
electrolytes since there solutions are good
conductors of electricity. Weak acid/base solutions
do not conduct electricity well and are called weak
electrolytes.
How do we tell if a solution conducts electricity?
7-5 Aqueous Ionic Compounds
Strong electrolyte
Weak electrolyte
Nonelectrolyte
7-5 Aqueous Ionic Compounds
Solutions are homogeneous mixtures of a
solute and a solvent.
• The solute is the solution component in the
smallest amount while the solvent is the larger
component of a solution.
• Solutes whose solutions conduct electricity are
called electrolytes
• Solutes whose solutions do not conduct electricity
are called nonelectrolytes
• Electrolytes are solutes that form ions when they
dissolve. Ionic solutes or acids usually form
solutions that conduct electricity.
7-5 Aqueous Ionic Compounds
There are some more specific rules that allows us to better
estimate the solubility of ionic compounds.
You will be given these if you need them.
7-6 Precipitation Reactions
Using the solubility rules on the previous slide
asign (s) and (aq) to the formulas for the following
equation
NaCl(?) + AgNO3(?)
AgCl(?) + NaNO3(?)
7-6 Precipitation Reactions
Using the solubility rules on the previous slide
asign (s) and (aq) to the formulas for the following
equation
NaCl(aq) + AgNO3(?)
AgCl(?) + NaNO3(?)
7-6 Precipitation Reactions
Using the solubility rules on the previous slide
asign (s) and (aq) to the formulas for the following
equation
NaCl(aq) + AgNO3(aq)
AgCl(?) + NaNO3(?)
7-6 Precipitation Reactions
Using the solubility rules on the previous slide
asign (s) and (aq) to the formulas for the following
equation
NaCl(aq) + AgNO3(aq)
AgCl(s) + NaNO3(?)
7-6 Precipitation Reactions
Using the solubility rules on the previous slide
asign (s) and (aq) to the formulas for the following
equation
NaCl(aq) + AgNO3(aq)
AgCl(s) + NaNO3(aq)
7-6 Precipitation Reactions
Using the solubility rules on the previous slide
asign (s) and (aq) to the formulas for the following
equation
NaCl(aq) + AgNO3(aq)
AgCl(s) + NaNO3(aq)
This is called a formula equation
7-6 Precipitation Reactions
Using the solubility rules on the previous slide
asign (s) and (aq) to the formulas for the following
equation
NaCl(aq) + AgNO3(aq)
AgCl(s) + NaNO3(aq)
This is called a formula equation
When Ionic solids and acids dissolve in water ions
are formed, and the aqueous formulas really do not
exist. A more realistic equation would be the ionic
equation.
7-6 Precipitation Reactions
NaCl(aq) + AgNO3(aq)
AgCl(s) + NaNO3(aq)
formula equation
Separating the aqueous substances into ions produces
an ionic equation.
Na+(aq) + Cl-(aq) + Ag+(aq)
AgCl(s) + Na+(aq) + NO3- (aq)
ionic equation
7-6 Precipitation Reactions
NaCl(aq) + AgNO3(aq)
AgCl(s) + NaNO3(aq)
formula equation
Separating the aqueous substances into ions produces
an ionic equation.
Na+(aq)+Cl-(aq)+Ag+(aq)+NO3-(aq)
AgCl(s)+Na+(aq)+NO3-(aq)
ionic equation
Substances found on both sides of the equation are
called spectator ions and are boxed above.
Eliminating the spectator ions generates the net ionic
equation.
Ag+ (aq) + Cl- (aq)
AgCl (s)
Net ionic equation
7-6 Precipitation Reactions
It is possible for all of the reactants and products
to be water soluble and thus produce all
spectator ions. If this is the case then all of the
ions cancel out and there is no net ionic
equation. When this occurs then we say that
there is No Reaction, and give the label NR.
7-6 Precipitation Reactions
Five Driving Forces Favor Chemical Change
1.
2.
3.
4.
5.
Formation of a solid (Precipitate formation)
Formation of water (acid base reactions)
Transfer of electrons (REDOX) reaction
Formation of a gas (many different types)
Formation of a weak electrolyte (formation weak
acids and bases)
7-6 Precipitation Reactions
Formation of water is a normal product
between acids and bases. Since acids and
bases dissolve in water to make solutions
that are electrolytes, then we conclude that
acids and bases have some ionic
character. Since water does not ionize, then
when water is formed, we will also have a
net ionic equation and then a chemical
reaction.
7-6 Precipitation Reactions
Strong acids and bases ionize 100%!
Memorized Strong acids and bases:
Acids
HCl (aq)
HI (aq)
HBr (aq)
HNO3
H2SO4
HClO4
Bases
Hydroxides of
group I and II
metals, except Be
and Mg
7-7 Aqueous Reactions
Acids undergo characteristic double replacement
reactions with oxides, hydroxides, carbonates and
bicarbonates.
2HCl (aq) + CuO (s)  CuCl2 (aq) + H2O (l)
2HCl (aq) + Ca(OH)2 (aq)  CaCl2 (aq) + 2H2O (l)
2HCl (aq) + CaCO3 (aq)  CaCl2 (aq) + H2O (l) + CO2 (g)
2HC l (aq) + Sr(HCO3)2 (aq)  SrCl2 (aq) + 2H2O (l) + 2CO2 (g)
7-8 Acid/Base Gas Evolution
Acids undergo characteristic double replacement
reactions with oxides, hydroxides, carbonates and
bicarbonates.
2HCl (aq) + CuO (s)  CuCl2 (aq) + H2O (l)
2HCl (aq) + Ca(OH)2 (aq)  CaCl2 (aq) + 2H2O (l)
2HCl(aq) +CaCO3(aq) CaCl2 (aq)+H2O (l) +CO2 (g)
2HC l(aq)+Sr(HCO3)2(aq)SrCl2 (aq)+2H2O(l)+ 2CO2
(g)
7-8 Acid/Base Gas Evolution
Bases undergo a double replacement reaction with
acids called neutralization:
NaOH (aq) + HCl (aq)  H2O (l) + NaC l (aq)
In words this well known reaction is often described as:
“acid plus base = salt plus water”
We previously discussed this reaction when describing
types of reactions.
7-8 Acid/Base Gas Evolution
We have discussed the double replacement reactions
and ionic equations before. Since the acids and
bases undergo double replacement reactions called
neutralization reactions, then they can have ionic
equations too.
Formula equation:
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
Total ionic equation:
H+ (aq) + Cl- (aq) + Na+ (aq) + OH- (aq)  Na+ (aq) + Cl- (aq) + H2O (l)
Net ionic equation:
H+ (aq) + OH- (aq)  H2O (l)
7-8 Acid/Base Gas Evolution
Another property of acids is their reaction with certain
metals to produce hydrogen gas, H2 (g).
Zn (s) + 2HC l (aq)  H2 (g) + ZnCl2 (aq)
This is an example of a single replacement reaction
and is a redox reaction.
Total ionic equation:
Zn (s) + 2H+ (aq) + 2Cl- (aq)  H2 (g) + Zn2+ (aq) + 2Cl- (aq)
Net ionic equation:
Zn (s) + 2H+ (aq)  H2 (g) + Zn2+ (aq)
The End