Chapter 5: Chemical Processes
Mini Investigation: The Burning Candle Riddle, page 191
A. Most students observed that the taller candle extinguished before the shorter candle.
B. The heat of the candles caused the carbon dioxide released during combustion to rise and
extinguish the taller candle first.
Section 5.1: The Combustion of Hydrocarbons
Mini Investigation: Exploring Bunsen Burner Combustion, page 195
A. Soot formation on the spoon was evidence of incomplete combustion.
B. The observation that the surface of the spoon remained clean when placed in the blue flame
was evidence of complete combustion.
C. Opening the air hole of the Bunsen burner allows more oxygen to enter the combustion area.
As a result, the combustion is more complete with the blue flame.
D. A car owner requires complete combustion in order to maximize the energy released and
minimize the fuel residue that may form on car engine components, making them less efficient.
Research This: Clean Coal—A Contradiction?, page 196
A. Answers may vary. Sample answer: Clean coal technology is any technology that is designed
to reduce the polluting emissions resulting from the combustion of coal. These emissions include
particulate matter, sulfur oxides and carbon dioxide. Some examples of clean coal technologies
include processes that remove sulfur impurities from coal prior to combustion. Others involve
collecting and treating pollutants before they are released into the environment. Carbon dioxide,
for example, can be collected and stored deep underground in depleted natural gas wells and
secure underground rock formations.
Critics of clean technologies argue that the combustion of coal, by its very nature, can never be
truly clean. Carbon dioxide, an important greenhouse gas, is generated in any combustion
process. Storing carbon dioxide underground is a costly process that is yet to be proven
completely effective.
B. Answers may vary. Some students may argue that given the importance of coal in generating
electricity, further investment in clean coal technology is warranted. However, a greater priority
should be to find alternative energy sources that are more sustainable.
Section 5.1 Questions, page 197
1. Complete combustion of a hydrocarbon fuel occurs when the oxygen supply is plentiful.
Incomplete combustion occurs when the oxygen supply is limited.
2. (a) 2 C4H10(g) + 13 O2(g) → 8 CO2(g) + 10 H2O(g)
(b) Using a butane stove inside a tent is not advisable because there may be combustible
materials inside. Furthermore, the supply of oxygen in the tent may be limited, which could
result in incomplete combustion and the production of hazardous carbon monoxide.
3. (a) The chemical formula of the hydrocarbon is C5H12.
(b) The chemical formula of the hydrocarbon is C9H20.
(c) The chemical formula of the hydrocarbon is C6H14.
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Chapter 5: Chemical Processes
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4. (a) The balanced chemical equation for the complete combustion of hexane is:
2 C6H14(g) + 19 O2(g) → 12 CO2(g) + 14 H2O(g)
(b) C6H14(g) + 8 O2(g) → 3 CO2(g) + 3 CO(g) + 7 H2O(g)
5. (a) A yellow/orange flame of a Bunsen burner is evidence of incomplete combustion.
(b) Black smoke coming out of an automobile’s exhaust tailpipe is evidence of incomplete
combustion.
(c) Traces of orange in the flame and a sooty residue in a gas fireplace are evidence of
incomplete combustion.
6. (a) A limited supply of oxygen indoors promotes incomplete combustion of propane, releasing
deadly carbon monoxide gas.
(b) As the truck driver presses on the gas pedal, the air/fuel mixture is initially rich with fuel,
resulting in incomplete combustion, which produces black smoke.
(c) The blue flame of a Bunsen burner is evidence of complete combustion. Adjusting the burner
allows more oxygen to enter the combustion area, making the combustion more complete.
(d) As the combustion of the candle uses up the oxygen in the jar, combustion becomes more
incomplete, releasing more smoke until the candle extinguishes.
7. (a) A “fuel-lean” mixture contains less fuel and more oxygen than a “fuel-rich” mixture.
(b) A “fuel-lean” mixture is more likely to undergo complete combustion because oxygen is
plentiful. A “fuel-rich” mixture is more likely to undergo incomplete combustion because the
supply of oxygen is limited.
8. The combustion in bonfires is usually incomplete. As a result, air pollutants such as smoke
and unknown combustion products are released into the environment. Bonfires are also a safety
hazard as they can easily get out of control if they are not monitored properly.
9. (a) Purchasing power of the consumer will decrease as the cost of fuel increases. More of the
consumer’s income will be spent on transportation costs. Furthermore, the increased cost of
hydrocarbon fuels will be incorporated into the cost of consumer goods.
(b) New neighbourhoods may be designed to be more concentrated so as to minimize the need
for automobiles and to make more efficient use of public transit.
(c) Locally produced goods may become more popular as the cost of goods produced in other
countries with cheap labour becomes more expensive due to transport costs.
10. Answers may vary. Sample answer: Centuries of air pollution and soot from the burning of
candles deposited a layer of soot on the frescoes. People in favour of the work cited that it would
restore the frescoes to the way Michelangelo had intended them to appear. Opponents to the
restoration were concerned that the restoration would damage the frescoes. Some also
complained that the darkened colours of frescoes prior to restoration better suited the Chapel
than the bright colours that lay beneath the layers of soot.
11. Answers may vary. Sample answers:
(a) False. Most cars need less than a minute to warm up.
(b) False. Restarting a car has little impact or wear on the engine.
(c) True
(d) False. Excess idling is a problem in all seasons.
(e) True
(f) True
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Chapter 5: Chemical Processes
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12. Answers may vary. Sample answer: Exposure to certain chemicals in the environment can
initiate certain types of cancer. However, there are many other factors that can contribute to the
risk of developing cancer, including genetics and lifestyle. Consequently, it is often difficult to
link exposure to a specific chemical to cancer.
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Chapter 5: Chemical Processes
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