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Science 30

Unit B – Chemistry and the Environment

Outcome 1: Students will analyze the sources of acids and bases and their effects on the

environment.

Specific Outcome 1.8: Outline the chemical reactions that produce air pollutants that, when

combined with water, ultimately result in acid deposition.

Textbook reference pages: p. 152 – 164 in Science 30

Products of Combustion Reactions

COMBUSTION REACTIONS

- COMBUSTION:

o Requires: Fuel and Oxygen

o Releases: Energy

- FOSSIL FUEL COMBUSTION:

o Reactants: hydrocarbon (ethane, propane, methane, etc.)

HYDROCARBONS are organic compounds that contain HYDROGEN and CARBON

atoms

o Products: CO2(g) + H2O(g) (possibly others, depending on impurities found in the

reactant)

Working as a team in a local dogsled race, Kayla and her dogs challenge the

cold and their physical limits. They are all working and breathing hard. With

each breather Kayla and her dogs take, they must exhale the products of

Cellular Respiration - a process that converts the chemical potential energy

within food into a form the body’s muscles can use.

Cellular Respiration – the process by which cells convert the chemical

energy stored in organic molecules (sugars) into energy that cells can use.

 - Reactants: Glucose (C6H12O6) + O2(g)

 - Products: CO2(g) + H2O(g) + ATP (energy)

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- CH4(g) + 2 O2(g) CO2(g) + 2 H20(g)

o Complete combustion occurs when there is sufficient enough oxygen O2(g)

- 2 CH4(g) + 3 O2(g) 2 CO(g) + 4 H20(g)

o Incomplete combustion occurs when there is a lack of O2(g)

o Produces  CO (Carbon Monoxide) along with CO2 (Carbon Dioxide)

- COMBUSTION, like any chemical reaction, involves collisions between the molecules of the

reactants.

o This results in the formation of CARBON DIOXIDE AND WATER (products).

Example:

 CH4(g) + O2(g) CO2(g) + H2O(g)

Emissions and Combustion

- During most combustion reactions, the oxides produced are released into the atmosphere.

o These are called EMISSIONS

Emissions include

a) oxides of CARBON

b) oxides of NITROGEN

c) oxides of SULFUR

Methane

(hydrocarbon)

Carbon Dioxide

Because we have a hydrocarbon

(methane) and it produces carbon

dioxide (NOT carbon monoxide), we

know this is COMPLETE

COMBUSTION

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OXIDES OF CARBON

1. Carbon Dioxide:

Carbon dioxide can enter our atmosphere through COMBUSTION and NATURAL SOURCES.

COMBUSTION:

- Burning carbon compounds (like wood and other forms of BIOMASS plant

matter/agricultural waste or hydrocarbon molecules) creates CARBON DIOXIDE

NATURAL SOURCES:

- Cellular Respiration, forest fires, volcanic eruptions and weather of some rocks releases carbon

dioxide into the atmosphere naturally. (CARBON CYCLE)

Problem with a buildup of carbon dioxide in the atmosphere

-  CO2 is a greenhouse gas (it holds in thermal energy. An increase in CO2 increases thermal

energy retention, which increases overall atmospheric temperatures)

http://www.interactiveoceans.washington.edu/story/Carbon%20Cycle

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2. Carbon Monoxide

- Carbon Monoxide is produced during combustion with limited  O2(g) (incomplete combustion)

- Where does carbon monoxide come from?

o AUTOMOBILE EMISSIONS (eg. Car engines)

- Problems with carbon monoxide?

o bonds to hemoglobin, preventing O2  from bonding, preventing O2(g) from reaching

body tissues, resulting in cell death

QUESTION:

A. Refer to the diagram of the carbon cycle on page 157. Explain how the increased use of

combustion processes by society and deforestation could result in a higher level of atmospheric

carbon dioxide, a level that cannot be removed by natural mechanisms.

An increase in combustion processes could result in an increase in the amount of carbon dioxide in

the atmosphere if the speed at which carbon dioxide is produced is greater than the speed at which

carbon dioxide can be removed from the atmosphere.

BALANCING CHEMICAL FORMULAS

- All chemical reactions must begin and end with the same atoms, in the same proportions

- Recall from earlier science courses, this requires you to balance all chemical equations

Examples:

1. 2 C2H6(g) + 7 O2(g) 4 CO2(g) + 6 H2O(g)

2. 1 CH4(g) + 2 O2(g) 1 CO2(g) + 2H2O(g)

3. 1 C5H12(g) + 8 O2(g) 5 CO2(g) + 6 H2O(g)

4. 1 C4H8(g) + 6 O2(g) 4 CO2(g) + 4 H2O(g)

5. 2 C4H10(g) + 13 O2(g) 8 CO2(g) + 10 H2O(g)

6. Combustion of Octane, C8H18(g)

2 C8H18(g) + 25 O2(g) 16 CO2(g) + 18 H2O(g)

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OXIDES OF SULFUR

Natural resources:

- Sulfur is an element that is found in small quantities within many HYDROCARBONS.

o Examples:

Coal (in Alberta) has low sulfur but in Eastern Canada, Coal has a higher sulfur

content

Crude oil and oil sands also have sulfur

Natural Gas has sulfur in the form of H2S (sour gas toxic to humans!)

SOUR GAS – natural gas that contains greater than 1% hydrogen sulfide

o SOUR GAS when processed and sent to your home, removes the

hydrogen sulfide through a process called SWEETENING. (YOU GET

RID OF THE SOUR AND MAKE IT SWEET)

o 40% of the natural gas reserves in Alberta are SOUR! We have a lot

of sweetening to do!

Sulfur dioxide (SO2) and Sulfur trioxide (SO3)

- Low quality natural gas is FLARED this process converts that

H2S (Sour Gas) to SO2 and SO3

o How the flaring process works:

Sour gas is mixed with water to produce either

sulfur dioxide or sulfur trioxide.

- Sulphur dioxide (SO2) and sulphur trioxide (SO3) gases are emitted into the atmosphere during the process that removes H2S(g) from natural gas.

- Another major source of SOX is the combustion of fossil fuels

containing sulphur

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Sulphur removed from sour gas in SW Alberta

OXIDES OF NITROGEN

Earth’s atmosphere is 78% NITROGEN (N2(g) – a

normally unreactive gas)

High temperatures of combustion cause

nitrogen to react, producing NO(g) (Nitrogen

monoxide) and NO2(g) (nitrogen dioxide)

o Oxides of nitrogen are commonly referred

to as NOx COMPOUNDS

o NOx emission levels tend to change

depending on:

COMBUSTION OF FOSSIL FUELS (they

are higher near urban areas)

SEASONS (temperature)

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• Sulphur oxides (SOX) and nitrogen oxides (NOX) in the atmosphere cause acid rain

Issues with Combustion:

1. METAL PARTICLES can be present in combustion emissions

a. Example: Coal contains trace amounts of both MERCURY AND LEAD

i. THESE POISON YOU!

2. PARTICULATE MATTER (small solids suspended in the atmosphere)

a. Soot, smoke, ash (from industry and forest fires), soil particles, pollen…

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i. These things contribute to asthma and other lung diseases.

Particulate Matter (PM)

Hydrocarbon combustion contributes to particulate matter – tiny particles suspended in the

atmosphere

PM can be smaller than the width of a human hair

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Practice questions:

Page 159 # 4 & 5

4. complete combustion: CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g)

incomplete combustion: 2 CH4(g) + 3 O2(g) 2 CO(g) + 4 H2O(g)

5. The complete combustion of methane uses more oxygen per molecule of methane, 2O2: 1CH4,

than the incomplete combustion of methane, 3O2: 2CH4 or 1.5O2: 1CH4.

Page 160, #7 & 8

7. Emissions of NOx are the result of vehicle emissions and combustion processes that use

atmospheric air (e.g., furnaces). The higher concentration of people in urban areas—homes,

vehicles, and so on—results in higher emissions. Also, large industries tend to be located near urban

areas, which adds to NOx emissions.

8. a. NOx emissions will increase. There are more vehicles on the road during rush hour.

b. NOx emissions will increase. A cold snap in winter increases furnace use to heat homes. It also

increases idling time of vehicles as they warm up.

c. NOx emissions will increase. A heat wave in summer increases the demand on power plants due to

the electricity needed to operate air conditioners.

Page 164, # 1-8

1. a. Combustion is a chemical process involving a reaction of a substance with oxygen.

Combustion is a major source of emissions.

b. An oxide is a chemical substance consisting of oxygen and another element. Many chemical

compounds are present as oxides (e.g., carbon dioxide, nitrogen oxides, and sulfur oxides) in

emissions.

c. Pollution consists of waste substances that contaminate or harm their surroundings. This lesson

describes some of the sources and common forms of pollution.

d. A greenhouse gas is a substance that is capable of absorbing infrared radiation (heat) and

preventing its loss. Greenhouse gases act to trap energy in the atmosphere, contributing to global

climate change. Carbon dioxide, a product of the combustion of hydrocarbons, is a greenhouse

gas.

e. Hemoglobin is a molecule in blood that is responsible for the transport of oxygen. Emissions like

carbon monoxide can bind to hemoglobin, affecting oxygen transport in the human body and, thus,

affecting health.

f. Sour gas is a natural gas containing hydrogen sulfide, H2S(g). A great deal of sour gas is extracted in

Alberta, and there may be concerns about the effects of this process on the environment.

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g. NOx represents the oxides of nitrogen—nitrogen monoxide, NO(g), and nitrogen dioxide, NO2(g)—

and is a by-product of combustion processes. Nitrogen is usually not present in the fuel, but it can be

a product of the process.

h. Particulate matter consists of tiny particles from emissions that are suspended in air. Particulate

matter may consist of larger particles and may be visible. It is significant because it is a health hazard.

i. A carcinogen is a substance that may cause cancer. Carcinogens are a major threat to health

and should be avoided.

2. Bonds between the atoms of the fuel are broken and new combinations between the atoms of

the fuel and (most often) oxygen form, releasing energy.

3. If carbon is in the substance being combusted, carbon monoxide and carbon dioxide may be

produced. Likewise, if sulfur is in the substance being combusted, sulfur dioxide may be produced.

4. Nitrogen oxides can appear in a variety of forms, like NO(g) and NO2(g). The subscript x refers to the

number of oxygen atoms that may be present.

5. a. 1 CH4(g) + 2 O2(g) 1 CO2(g) + 2 H2O(g)

b. 2 C2H6(g) + 7 O2(g) 4 CO2(g) + 6 H2O(g)

c. 1 C3H8(g) + 5 O2(g) 3 CO2(g) + 4 H2O(g)

6. The air drawn into internal combustion engines consists mostly of nitrogen. Some of the energy

released by the combustion process enables the combination of nitrogen and oxygen to form NOx

compounds.

7. a. thermal step: 2 H2S(g) + O2(g) 2 S(s) + 2 H2O(g)

2 H2S(g) + 3 O2(g) 2 SO2(g) + 2 H2O(g)

catalytic step: 2 H2S(g) + SO2(g) 3 S(s) + 2 H2O(g)

b. NOx compounds are produced in the thermal step. The high-temperature combustion process

uses atmospheric air in the combustion chamber (like most furnaces).

c. Using pure oxygen will remove nitrogen from the combustion chamber. If nitrogen is not present in

the combustion chamber, the emission of NOx compounds is avoided.