Chapter 9
Classifying Chemical
Reactions
Types of Reactions
•
We will consider five types of reactions :
1.
2.
3.
4.
5.
Single displacement reactions
Double displacement reactions
Decomposition reactions
Synthesis reactions
Combustion reactions
1. Single Replacement Reactions
• Single Replacement Reactions occur when
one element replaces another in a compound.
• A metal can replace a metal (+) OR
a nonmetal can replace a nonmetal (-).
• element + compound compound + element
A + BC  AC + B (if A is a metal) OR
A + BC  BA + C (if A is a nonmetal)
(remember the cation always goes first!)
In a single replacement reaction it is better to
write H2O as HOH because it will split into
H+ and OH- (not H+ and O2- !!)
Single Replacement
• A small piece of lithium metal is added to water.
Single Replacement Reaction
Single Replacement Reactions
• Sodium chloride solid reacts with fluorine gas
NaCl(s) + F2(g)  NaF(s) + Cl2(g)
unbalanced
Single Replacement Reactions
• Zinc metal reacts with aqueous nickel (II) nitrate
Zn(s)+ Ni(NO3)2(aq) Zn(NO3)2(aq) + Ni(s)
2. Double Replacement Reactions
• Double Replacement Reactions occur when
the cations in two compounds switch places.
• compound + compound  compound + compound
• AB + CD  AD + CB
Double Replacement Reactions
• KOH + H2SO4 → K2SO4 + HOH
• FeS + HCl → FeCl2 + H2S
• NaCl + H2SO4 → Na2SO4 + HCl
• NH4NO3 + NaCl → NH4Cl + NaNO3
Decomposition Reactions
• Decomposition reactions occur when a compound
breaks up into two or more substances.
• Some examples of decomposition reactions are:
– Potassium chlorate when heated breaks into oxygen gas
and potassium chloride.
∆
• 2KClO3 → 2KCl + 3O2
– Heating sodium bicarbonate decomposes into sodium
carbonate and water and carbon dioxide.
∆ 3Na CO + 3H O + 3CO
• 6NaHCO3 →
2
3
2
2
3. Decomposition Reactions
• The simplest decomposition reactions
occur when a binary compound breaks
up into its elements.
Compound  Element + Element
• In general: AB  A + B
• Example: 2 H2O  2H2 + O2
• Example: 2 HgO  2Hg + O2
Decomposition Reaction
This reaction is highly endothermic
Energy Changes
• “Many” decomposition reactions involve
large changes in energy (they are highly
endothermic or highly exothermic).
Toluene
A
A
A
Trinitrotoluene
Tri-Nitro-Toluene
Nitroglycerin
Nitroglycerin is a contact explosive (physical shock can cause
it to explode) and it degrades over time to even more unstable
forms. This makes it extremely dangerous to transport or use.
Alfred Nobel
• Nobel found that when
nitroglycerin was added to
an absorbent inert
substance it became safer.
• He patented this in 1867
as dynamite.
Alfred Nobel
“The Merchant of Death is Dead”
Alfred Nobel
“The Merchant of Death is Dead”
• The erroneous publication in 1888 of a
premature obituary of Alfred Nobel by a French
newspaper, condemning him for his invention of
dynamite, is said to have brought about his
decision to leave a better legacy after his death.
• The obituary stated "The merchant of death is
dead" and went on to say, "Dr. Alfred Nobel,
who became rich by finding ways to kill more
people faster than ever before, died yesterday.”
• In reality the newspaper had instead confused
Alfred for his brother who had passed away.
Nobel Prizes
• Nobel signed his last
will and testament
and set aside the bulk
of his estate to
establish the Nobel
Prizes.
Synthesis Reactions
• Synthesis reactions occur when two or more
substances combine to form a compound.
(Sometimes these are called combination or
addition reactions.)
– sulfur trioxide reacts with water to make
sulfuric acid.
• H2O + SO3 → H2SO4
4. Synthesis reactions
• The simplest Synthesis reactions occur
when two elements combine and form a
binary compound.
element + element  compound
• Basically: A + B  AB
• Example: 2H2 + O2  2H2O
• Example: Fe + Cl2  FeCl2
Synthesis Reaction
5. Combustion Reactions
• Combustion reactions
occur when a hydrocarbon
reacts with oxygen gas.
• This is also called
burning!!!
• The products of
combustion are carbon
dioxide and water.
Combustion
Reactions
• Example:
- CxHy + O2  CO2 + H2O
• Combustion is used to
heat homes and run
automobiles (example:
octane in gasoline, is
C8H18).
• Combustion also got you
to school today.
Cellular Respiration
C6H12O6 + 6O2 →
6CO2 + 6H2O
Combustion Reactions
• CxHy + O2  CO2 + H2O
• This is an example of complete
combustion.
• Products in complete combustion
are “ALWAYS” carbon dioxide
and water.
• Combustion may also be
incomplete in which other
products will form .
Complete vs. Incomplete
Combustion
• Determined by the amount of oxygen.
• Incomplete combustion occurs when there
isn't enough oxygen to allow the fuel
(usually a hydrocarbon) to react
completely.
Incomplete Combustion
• Incomplete Combustion occurs when hydrocarbons are
burned in limited oxygen
• Either we limit the oxygen available or there is simply
not enough oxygen – think of a car running in an
enclosed garage.
• we produce carbon monoxide instead of carbon
dioxide, or in extremely limited oxygen we produce pure
carbon (soot).
• 2C3H8 + 7O2 → 6CO + 8H2O (limited oxygen)
• C3H8 + 2O2 → 3C + 4H2O (extremely limited oxygen)
Complete and Incomplete
Combustion
• In most combustion reactions both
incomplete and complete combustion
occur at the same time and so we form all
the previously mentioned products.
C9H20 + O2 → CO2 + CO + C + H2O
Complete and Incomplete
Combustion
• We will however consider combustion to
be complete when predicting the products
of reactions.
C9H20 + O2 →
C9H20 + O2 → CO2 + H2O
Gas Lighting and CO
Poisoning
• People who lived in 19th
century cities were often
poisoned by exposure to
carbon monoxide from
illuminating gas, which
was a flammable mixture
of gas suitable for
lighting purposes that is
made from coal and
contained extremely high
levels of CO.
Poe's face has one eye
drooping lower than the other
while his mouth slants the other
way. This same abnormality
can be seen in the faces of
people poisoned by CO
today. It is caused by the effect
of repeated CO exposure on
facial nerves and can be
partially if not completely
reversed with months of daily
oxygen therapy.(very high levels
of CO exposure, in comparison,
can cause complete paralysis or
coma)
Was Poe suffering from CO
poisoning or just a troubled soul?
• Poe described many
symptoms of CO
poisoning in his letters,
poems and tales.
• People poisoned by
CO often have the
same bizarre physical
and mental symptoms
he describes.