Chemical Reactions and
Equations
Chapter 6
Objectives
• 6.1 Relate chemical changes and macroscopic
properties.
• 6.1 Demonstrate how chemical equations
describe chemical reactions
• 6.1 Illustrate how to balance chemical
reactions by changing coefficients
Objectives
• 6.2 Distinguish among the five major types of
chemical reactions
• 6.2 Classify a reaction as belonging to one of
five major types
• 6.2 Predict the products of chemical reactions
Balancing Chemical Equations
• CH4 (g) + O2 (g) CO2 (g) + H2O (l)
– Reactants  Products
• Coefficients. Change these to change how
many of the molecule you want
– CH4 + 2 O2  CO2 + 2 H2O
• Do not change the subscripts, the molecule is
what it is
– CH4 + 2 O2  CO2 + 2 H2O
States of Matter
•
•
•
•
•
CH4 (g) + O2 (g) CO2 (g) + H2O (l)
(g) = Gas
(l) = Liquid (pure)
(s) = Solid
(aq) = Aqueous (Dissolved in water)
Balance by Guess and Check
• Keep track of number of atoms on each side
• H2 + N2  NH3
• Reactants
–2H
–2N
Products
3H
1N
• Change coefficient and count again
Energy
• Endothermic: Energy is a reactant
– In later courses (or this year ) we will discuss the
actual numbers
• Exothermic: Energy is a product
– Mg + O  MgO + Energy (Heat)
Evidence of Chemical Change
– Four Evidences
•
•
•
•
Change in energy (heat/cold/light)
Change in color
Precipitate formed (solid)
Gas formed (but not due to heat)
38
Types of Chemical Reactions
• 5 chemical reactions
– Synthesis
– Decomposition
– Single Displacement
– Double Displacement
– Combustion
Types: Synthesis
Example C + O2
C + O O 
O C O
C
CC
C
O O
C
O O
C
C C C C C C
CC
General:
A + B  AB
Types: Decomposition
Example: NaCl
Cl
Na

General:
Cl
+
Na
AB  A + B
Types: Decomposition
Example 2HgO
O Hg

O Hg
General:
Hg
Hg
+
O O
AB  A + B
Types: Single displacement
Example: Zn + CuCl2
Cl
Cu
Zn
+
Cl
General:

Cl
Zn
Cu
+
Cl
AB + C  AC + B
Types: Double displacement
Example: MgO + CaS
Mg
O
+
Ca
S
General:

Mg
S
+
Ca
O
AB + CD  AD + CB
The 5 reactions you must know (for now)
combustion: AB + oxygen  oxides of A & B
synthesis: A + B  C
decomposition: AB  A + B
single displacement: A + BC  AC + B
double displacement: AB + CD  AD + CB
What type of Reaction?
a)Mg + HCl  MgCl2 + H2
b) Ca + N2  Ca3N2
c) NH4NO3  N2O + H2O
d) BiCl3 + H2S  Bi2S3 + HCl
e) C4H10 + O2  CO2 + H2O
f)
O2 + C6H12O6  CO2 + H2O
g) NO2 + H2O  HNO3 + NO
h)Cr2(SO4)3+ NaOH  Cr(OH)3+ Na2SO4
i) Al4C3 + H2O  CH4 + Al(OH)3
What type of reaction?
• Sodium (s) + Chlorine (g) 
– Sodium Chloride (s)
• Calcium Carbonate (s) 
– Calcium Oxide (s) + Carbon Dioxide (g)
• C3H8 (g) + O2 
– CO2 + H2O
• Phosphorus pentachloride (s) 
– Phosphorus trichloride (s) + Chlorine (g)
What type of reaction?
• Nitrogen Monoxide (g) + Ozone (g) 
– Nitrogen dioxide (g) + Oxygen (g)
• Chlorine (g) + Ozone (g) 
– Hypochlorite (g) + Oxygen (g)
• Silver Nitrate (aq) + Barium Chloride (s)
–  Silver Chloride (s) + Barium Nitrate (aq)
• Calcium Oxide (s) + water (l) 
– Calcium Hydroxide (s)
Predict the Products
• NaCl + Ag react in a single displacement
reaction, what is the product?
– Switch the metals
• Potassium (K) and Oxygen react in a synthesis
reaction, what is the product?
– Make an ionic compound
• Oxygen and Methane react in a combustion
reaction, what is the product?
– Water and Carbon Dioxide
Objectives
• 6.3 Demonstrate factors that influence the
direction of a reaction.
• 6.3 Classify factors that influence the rate of a
reaction.
• 6.3 Writing Equilibrium expressions
Introduction
• Some chemical reactions are fast and some
are slow
• Which of the below are fast and which are
slow?
– Rusting of Iron
– Firecracker explosion
– Food becoming rotten
– Diamond turning into graphite
Factors Influencing Rate of Reaction:
Temperature
• Temperature
• Increase Temp  Increase Rate
– Putting food into the fridge slows down the
decomposition
– Cold-blooded reptiles sunbathing
– General rule of Thumb: Every 10 Celsius = 2x the
rate
Factors Influencing Rate of Reaction:
Pressure
• Pressure
• Increase Pressure  Increase Rate
• Only for gases
– Increased Pressure means increased rate of
chemicals colliding with one another
Factors Influencing Rate of Reaction:
Concentration
• Concentration
• Increase Concentration  Increase Rate
– Due to more molecules per volume
Factors Influencing Rate of Reaction: Surface
Area
• Surface Area
• Increase Surface Area  Increase Rate
– Grain elevator explosions (fine powder = lots of
surface area)
– When starting a fire, you begin with small pieces
of timber
Chemical Engineering
– These factors are very important to chemical
engineers who are responsible for producing
much of the chemicals we use.
– The speed and ease with which it can be made
often determine the cost.
Chemical Equilibrium
Dynamic Equilibrium
Major Ideas
• Completion reactions
• Reversible Reactions
• Dynamic Equilibrium
Chemical Reactions
– Up until now, we have only considered reactions
that only go one direction.
• This unit we will consider reactions that go
both directions, called reversible reactions.
The Difference
• Reversible Reaction:
– Reactants  Products and
– Products  Reactants
• Completion Reaction:
– Reactants  Products only
Completion/Reversible
• What does this mean? In any chemical
reaction, it is a competition between two
competing reactions. In a completion
reaction, one side wins big. In a reversible
reaction, the contest is more evenly matched.
Consider the following Completion reaction
• HCl (aq) + H2O (l)  H3O+ (aq) + Cl- (aq)
• When a HCl and water come into contact, the
H leaves the Cl and joins the water.
• When a Hydronium comes into contact with a
Cl-, the H doesn’t come back to the Cl-.
Why Not?
• Strength of Bonds (Enthalpy)
– If a chemical is produced which has a very strong
bond, then the molecule will not be broken apart
• Increased disorder on product side (Entropy)
– Haven’t discussed this yet, but chemical reactions
are more likely to occur when disorder increases
Consider the following Reversible
Reaction
• Ca+2 (aq) + SO4-2 (aq)  CaSO4 (s)
• The calcium ion and sulfate ion are trying to
react to make a solid. The solid is
decomposing to try to make the ions. This is a
reversible reaction because neither side wins
all the time
Dynamic Equilibrium
• Eventually, over time, the reversible reaction
will find some concentration where both sides
are reacting at the same rate. Even when
chemical reactions appear to have stopped,
the battle rages on.
– Static Equilibrium: You sit on a chair (force of
gravity = force of chair on you)
– Dynamic Equilibrium: Equal rate of reaction
• NOT necessarily equal amounts of Reactants/Products
Equilibrium = Equal Rates
• At Equilibrium, the forward and reverse
reaction are occurring at the same rate
• When a Calcium Sulfate solution reaches
equilibrium, for every Calcium and Sulfate that
combine, one Solid Calcium Sulfate
decomposes.
Reaching Equilibrium
Another Example
Completion Reaction
Products Favored
Both equally favored
Reactants Favored
Changing the direction or who is
favored
•
•
•
•
•
Add Reactants 
Add Products 
If endothermic, add heat (increase Temp) 
If exothermic, take away heat 
If gases present, increasing pressure favors
side with fewer gas molecules
Other Related Ideas
• Activation Energy: The amount of energy the
particles need when colliding for the atoms to
rearrange
• Reaction Rate: Related to Activation Energy
– Fast Reaction Rates generally means low
activation energy
– Slow Reaction Rates generally mean high
activation energies
Other related ideas
• Catalyst: Speed up reaction by lowering
activation energy
– Participate in helping reaction, but are not
changed by reaction
• Inhibitor: Slow down reaction
• Enzyme: Biological Catalyst
Practice Question
• N2 (g) + 3 H2 (g) 2 NH3 (g)
– How will the reaction react to …
•
•
•
•
•
a) Addition of Nitrogen gas?
b) Removal of Hydrogen gas?
c) Increase in Temperature?
d) Increase in Pressure?
e) What are the best conditions for the
production of ammonia, considering pressure
and temperature?
Practice Question
• 3 Fe(s) + 4 H2O (g) Fe3O4 (s) + 4 H2 (g) +
heat
• a) Increase the amount of water
• b) Decrease the volume by half
• c) Remove Fe3O4 as it is formed
• d) Add hydrogen to the mixture
• e) Increase the temperature
• f) Adding a catalyst
• Non-Athlete  Athlete
• Hungry Student  Full Student
• Demo
– [Cu(H2O)4]+2 (aq) + 4 Cl-1 
– [CuCl4]-2 (aq) + 4 H2O (l)