Combustion Reactions
 Combustion reactions
occur when a hydrocarbon
reacts with oxygen gas.
 This is also called
burning!!! In order to burn
something you need the 3
things in the “fire triangle”:
1) A Fuel (hydrocarbon)
2) Oxygen to burn it with
3) Something to ignite the
reaction (spark)
Combustion Reactions
• In general:
CxHy + O2  CO2 + H2O
• Products in combustion are
ALWAYS carbon dioxide and
water. (although incomplete
burning does cause some
by-products like carbon
monoxide)
• Combustion is used to heat
homes and run automobiles
(octane, as in gasoline, is
C8H18)
Balancing Combustion Reactions
1. Balance Carbon first
2. Balance Hydrogen next
3. Balance Oxygen (because it is alone on the
reactants side)
4. If the Oxygen cannot balance with whole
numbers, place the next integer in front of
the fuel and redo steps 1-3 until the equation
is balanced. You may have to repeat this
several times before your equation is
balanced.
1. Natural gas (methane) is burned in
furnaces to heat homes.
CH4 + O2  CO2 + 2H2O + energy
2. An acetylene torch is used to weld
metals together.
2C2H2 + 5O2  4CO2 + 2H2O + energy
3. Carbohydrates like glucose combine
with oxygen in our body to release
energy.
Acetylene torch
C6H12O6 + 6O2  6CO2 + 6H2O + energy
See page 264
(c) McGraw Hill Ryerson
2007
Examples of Reactions
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
2C4H10(g) +13O2(g)  8CO2(g) +10H2O(g)
2CH3OH(g) + 3O2(g)  2CO2(g) + 4H2O(g)
2C3H8(g) + 7O2(g)  6CO(g) + 8H2O(g)
Practice Reactions
 Predict products for the following
 Balance the reactions
C6H12O6 (s)+ 6 O2 (g)  6 CO2(g) + 6 H2O(g)
2 C7H14(l) +21 O2 (g)  14 CO2 (g)
+14 H2O(g)
Two Types of Combustion
 Complete “IDEAL”
 Incomplete “REAL”
 Clean combustion
with a hydrocarbon
produces carbon
dioxide and water
 Dirty combustion With
a hydrocarbon
produces carbon
and/or carbon
monoxide as well as
carbon dioxide
Combustion
• Example
•
C5H12 + 8 O2  5 CO2 +6 H2O
• Write the products and balance the
following combustion reaction:
•
C10H22 + O2 
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Combustion Reactions &
Vehicle Emissions
Cough, cough, hack, choke, cough, hack…..
10
What is Combustion?
 Combustion occurs when a fuel reacts
with oxygen to give off heat and light.
*Air provides enough oxygen (~20% oxygen, ~80% nitrogen)
 Fuels are typically made of carbon and
hydrogen (hydrocarbons)
What are some common fuels?
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Why Do We Care?
 Burning of fuel is the energy source for almost all types
of automobiles & Industrial processes
 Combustion accounts for 85% of all worldwide electricity
production
Source:
http://www.sunocoinc.com/market/marketplace.htm
Source:
http://museum.nist.gov/exhibits/timeline/item.cfm?itemId=27
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BUT,
 Combustion accounts for 90% of all airborne
pollution
 Air pollution can lead to lung problems and shorter
life spans…not to mention, acid rain
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Ideal Combustion aka (Complete Combustion)
 Ideal combustion produces only carbon dioxide,
water, and ENERGY:
 It occurs when there is sufficient oxygen for the
fuel to burn completely
Natural Gas:
CH4 + 2 O2  CO2 + H2O + energy
Gasoline (approximate):
C8H16 + 12 O2 8 CO2 + 8 H2O + energy
Glucose in your blood/muscles:
C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy
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Real Combustion aka “not ideal”
The combustion process is NEVER
complete and NEVER ideal
Occurs when the supply of oxygen is
limited
Flames resulting from incomplete
combustion are sooty, yellow and cooler
than complete combustion flames
Incomplete combustion cannot be
represented by a single balanced equation
Incomplete combustion produces products
such as….
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Primary Emissions from Automobiles
 Oxides of Carbon(CO, CO2)
 Oxides of nitrogen (NO, NO2)
 Oxides of sulfur (SO, SO2, SO3)
 Carbon as soot or particulates (C)
 Unburned fuel (hydrocarbons, CxHy)
 Water (H2O)
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Real Combustion aka “not ideal”
Fuel does not exist as a pure substance, it
contains other elements that can react in
side reactions and produce more than just
CO2 and H2O
Varying length of hydrocarbon chains
*Jet and diesel fuel contain hydrocarbon chains of 12 to
20 carbons in length. Fuel oil contains hydrocarbons 20
to 40 carbons long.
sulfur (S)
nitrogen (N)
oxygen (O)
CETP BASIC PRINCIPLES AND PRACTICES OF PROPANE
Products of Incomplete Combustion
Incomplete combustion is not only
inefficient but also dangerous.
Without enough air during
combustion, other products can
result, such as:
 Aldehydes: A toxic gas detectable by smell
 Excessive water vapor: Can be harmful to
appliances’ venting systems
 Soot: Potentially damaging to property
 Carbon monoxide: A highly toxic gas
undetectable by smell
Carbon monoxide is the most hazardous
product of incomplete combustion and can
immediately
harm people and animals.
LESSON 2
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Emissions: Automobiles
•Let’s look at what happens in ideal and real
combustion in automobiles. The symbols we will use
are shown below:
 Hydrogen (H)
 Nitrogen (N)
 Carbon (C)
 Oxygen (O)
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Ideal vs. Real Combustion
Oxygen
Nitrogen
Ideal
Carbon
dioxide
Carbon
dioxide
Real
Hydrocarbon
Water
Nitrogen
Water
Carbon monoxide
Unburned hydrocarbon
Nitrogen
Nitrogen dioxide
Nitrogen monoxide
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Products of Ideal combustion are not
harmful…but…
Products of real combustion are nonmetal oxides…what happens when they
get released into the atmosphere and
contact water vapour?
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Oxides (the synthesis story is not over)
An oxide is a compound of any element
combined with oxygen
Oxides form when an element reacts with
oxygen (usually in the air)
eg.
2 Mg (s) + O2 (g)  2 MgO (s)
N2 (g) + O2 (g)  NO2 or NO3 or NO or…NOx
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Properties of Oxides
Non-metal + Oxygen
 Non-metals react with
oxygen to produce nonmetallic oxides which are
gases at room
temperature.
Metal + Oxygen
 Metals react to produce
metallic oxides which tend
to be ionic solids at room
temperature.
 S (s) + O2 (g)  SO2 (g)
 Ca (s) + O2 (g)  CaO (s)
Oxides on their own are not a big problem,
except…..
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Oxides + Water
produce strong acids and bases
Non-metal oxide + water
 When dissolved in water
non-metal oxides from
acids.
Metal Oxide + water
 When dissolved in water
metal oxides form bases.
 SO2 (g) + H2O (l)  H2SO4 (aq)
 CaO (s) + H2O (l)  Ca(OH)2 (aq)
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Carbon Oxides, COx
C + O2  COx
CARBON MONOXIDE
 CO is POISIONOUS because it reduces the ability of
blood to bring oxygen to the body’s cells and tissues.
Remember that oxygen is needed for the combustion that gives our
bodies energy.
Motor vehicle exhaust contributes 60% of
all CO emissions
Carbon Monoxide
 Carbon monoxide is an odourless, tasteless,
colourless gas produced by the incomplete
combustion of carbon compounds.
 It is toxic to humans and can result in death if
you are exposed to it for long periods of time.
 Carbon monoxide will “stick” to your red
blood cells better than Oxygen will, and
therefore you will die from lack of Oxygen.
 Symptoms of CO poisoning include
headache, blue lips and nailbeds, nausea,
confusion.
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Carbon Dioxide
 CO2 is relatively harmless in small quantities that
we encounter it in the air
 The main concern with CO2 is its greenhouse
effect on the earth, trapping heat in the
atmosphere and changing global climates
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Nitrogen Oxides, NOx
N2 + O2  NOx
 NOx is used to describe NO, NO2 and other
oxides of nitrogen
 NO2 can be seen as a reddish brown layer of air
over cities
 NOx forms when fuel is burned at high
temperatures
 Primary sources are motor vehicles, electric
utilities
 2NO2 (g) + H2O(l)  HNO3(aq) +HNO2(aq)
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NO2 in the atmosphere
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Effects of Acid Rain
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Nitrogen Oxides
Environmental Effects:
NO2 is an component of acid rain
• can damage trees and lakes
NOX reacts with other chemicals (VOC’s,
volatile organic chemicals) in sunlight to
produce ozone
Good ozone occurs naturally above the earth
in the stratosphere, ozone near the ground is
toxic and is the main component of smog
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Nitrogen Oxides
Health Effects:
Lung damage
Illnesses such as asthma, bronchitis, and
emphysema
• (sicknesses caused by problems with breathing
passages and lungs)
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Catalytic Convertors
Modern vehicles are equipped with
catalytic convertors that capture the NOx
molecules before they are discharged into
the atmosphere
The interior of the convertor is coated with
a catalyst (palladium, platinum or rhodium)
that react to turn the NOx molecules back
into N2 and O2
2NO(g)  N2(g) + O2(g)
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Sulfur Oxides, SOx
S + O2  SOx
 SOx are colourless gases formed by burning
fuels containing sulfur such as coal and oil, and
from industries that use metallic ore, coal or
crude oil for their processes
 SO2 dissolves in water vapour to form acid and
interacts with other gases and particles in the air
to form sulfates which can be harmful to people
and the environment.
 SO2(g) + H2O(l)  H2SO4(aq)
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What are we doing about this?
Decreased allowable air emission levels
for COx, SOx and NOx in Industry.
Enforced emission testing for all vehicles
Alternative clean-burning fuels (H2) or
using renewable energy (electric cars.)
Industrial “Scrubbers” are systems that inject a
dry reagent or liquid into a dirty exhaust stream to "wash
out" acid gases & particulates before they are released
into the air.
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Other combustion hazards
Incomplete combustion
Can be a problem in enclosed spaces
Idling cars are not burning fuel efficiently and
therefore produce large amounts of CO and
other toxic gases
Soot from incomplete combustion is an
inhalation hazard
CO is the “silent killer”
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Other combustion hazards
House fires and fire fighting
Increased use of synthetic materials in the
household produce extremely toxic gases and
particles when they burn
Firefighters wear sealed breathing apparatus to
avoid inhaling the toxins, but some of the toxins
are absorbed through the skin causing health
risks to the firefighters
toxic gases in house fires
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homework
Read 5.3
Pg 204 # 3-6
Oxides worksheet