1 of 47© Boardworks Ltd 2009. 2 of 47© Boardworks Ltd 2009

1 of 47 © Boardworks Ltd 2009



The internal combustion engine: carbon

Alkanes with chain lengths of 5–10 carbon atoms are used as fuels in internal combustion engines.

This releases carbon dioxide into the atmosphere:

nonane + oxygen → carbon dioxide + water

C9H20(g) + 14O2(g) → 9CO2(g) + 10H2O(g)

Although modern internal combustion engines are more efficient than in the past, incomplete combustion still occurs:

nonane + oxygen → carbon monoxide + water

2C9H20(g) + 19O2(g) → 18CO(g) + 20H2O(g)


The temperature in an internal combustion engine can reach over 2000 °C. Here, nitrogen and oxygen, which at normal temperatures don’t react, combine to form nitrogen monoxide:

The internal combustion engine: nitrogen

N2(g) + O2(g) → 2NO(g)

Nitrogen monoxide reacts further forming nitrogen dioxide:

2NO(g) + O2(g) → 2NO2(g)

Nitrogen dioxide gas reacts with rain water and more oxygen to form nitric acid, which contributes to acid rain:

4NO2(g) + 2H2O(l) + O2(g) → 4HNO3(aq)


Incomplete combustion

If oxygen is limited then incomplete combustion will occur:

alkane + oxygen → carbon monoxide + water

alkane + oxygen → carbon + water

For example:

propane + oxygen → carbon monoxide + water

C3H8(g) + 3½O2(g) → 3CO(g) + 4H2O(g)

propane + oxygen → carbon + water

C3H8(g) + 2O2(g) → 3C(s) + 4H2O(g)






C9H20(g) + 14O2(g) → 9CO2(g) + 10H2O(g)



2C9H20(g) + 19O2(g) → 18CO(g) + 20H2O(g)


Pollutant gases






For example:


C3H8(g) + 3½O2(g) → 3CO(g) + 4H2O(g)


C3H8(g) + 2O2(g) → 3C(s) + 4H2O(g)






C9H20(g) + 14O2(g) → 9CO2(g) + 10H2O(g)



2C9H20(g) + 19O2(g) → 18CO(g) + 20H2O(g)


The catalytic converter


Pollutant gases






For example:


C3H8(g) + 3½O2(g) → 3CO(g) + 4H2O(g)


C3H8(g) + 2O2(g) → 3C(s) + 4H2O(g)






C9H20(g) + 14O2(g) → 9CO2(g) + 10H2O(g)



2C9H20(g) + 19O2(g) → 18CO(g) + 20H2O(g)




Sulfur contamination of fossil fuels

Sulfur is found as an impurity in crude oil and other fossil fuels. It burns in oxygen to form sulfur dioxide:

S(s) + O2(g) → SO2(g)

Sulfur dioxide may be oxidized to sulfur trioxide:

2SO2(g) + O2(g) → 2SO3(g)

Both of these oxides dissolve in water forming acidic solutions:

SO2(g) + H2O(l) → H2SO3(aq)



Pollutant gases






For example:


C3H8(g) + 3½O2(g) → 3CO(g) + 4H2O(g)


C3H8(g) + 2O2(g) → 3C(s) + 4H2O(g)






C9H20(g) + 14O2(g) → 9CO2(g) + 10H2O(g)



2C9H20(g) + 19O2(g) → 18CO(g) + 20H2O(g)






S(s) + O2(g) → SO2(g)


2SO2(g) + O2(g) → 2SO3(g)





What is acid rain?

Acid rain is caused by acidic non-metal oxides such as sulfur oxides and nitrogen oxides dissolving in rain water.

Rain water is naturally acidic because carbon dioxide dissolves in it, forming weak carbonic acid. However, sulfur and nitrogen oxides form more acidic solutions, which can damage trees and affect aquatic life in lakes and rivers.


Pollutant gases






For example:


C3H8(g) + 3½O2(g) → 3CO(g) + 4H2O(g)


C3H8(g) + 2O2(g) → 3C(s) + 4H2O(g)






C9H20(g) + 14O2(g) → 9CO2(g) + 10H2O(g)



2C9H20(g) + 19O2(g) → 18CO(g) + 20H2O(g)






S(s) + O2(g) → SO2(g)


2SO2(g) + O2(g) → 2SO3(g)





What is acid rain?




Removing sulfur dioxide pollution

Sulfur dioxide emissions from vehicle fuels such as petrol and diesel are reduced by removing nearly all of the sulfur impurities from the fuel before it is burnt.

Removing the sulfur from coal before it is burnt is not practical. Instead, the acidic sulfur oxides are removed from the waste gases using a base such as calcium oxide.


Pollutant gases






For example:


C3H8(g) + 3½O2(g) → 3CO(g) + 4H2O(g)


C3H8(g) + 2O2(g) → 3C(s) + 4H2O(g)






C9H20(g) + 14O2(g) → 9CO2(g) + 10H2O(g)



2C9H20(g) + 19O2(g) → 18CO(g) + 20H2O(g)






S(s) + O2(g) → SO2(g)


2SO2(g) + O2(g) → 2SO3(g)





What is acid rain?








Carbon dioxide in the atmosphere

Burning fossil fuels releases carbon dioxide into the atmosphere.

It has been suggested that increases in the amount of carbon dioxide and other greenhouse gases may be responsible for apparent changes to the climate.

Fossil fuels are being burned faster than they are being formed, which means that their combustion leads to a net increase in the amount of atmospheric carbon dioxide.


Pollutant gases






For example:


C3H8(g) + 3½O2(g) → 3CO(g) + 4H2O(g)


C3H8(g) + 2O2(g) → 3C(s) + 4H2O(g)






C9H20(g) + 14O2(g) → 9CO2(g) + 10H2O(g)



2C9H20(g) + 19O2(g) → 18CO(g) + 20H2O(g)






S(s) + O2(g) → SO2(g)


2SO2(g) + O2(g) → 2SO3(g)





What is acid rain?








Carbon dioxide in the atmosphere

Burning fossil fuels releases carbon dioxide into the atmosphere.

It has been suggested that increases in the amount of carbon dioxide and other greenhouse gases may be responsible for apparent changes to the climate.

Fossil fuels are being burned faster than they are being formed, which means that their combustion leads to a net increase in the amount of atmospheric carbon dioxide.


Greenhouse gases

Carbon dioxide, water vapour and methane have been described as the main greenhouse gases.

The greenhouse effect is a theory that has been suggested to explain apparent rises in the average temperature of the Earth.

This is because these have been suggested as the gases responsible for the majority of the greenhouse effect.

Increasing the amount of any of the greenhouse gases traps more heat energy from the Sun in the Earth’s atmosphere, raising the average temperature.


Pollutant gases


Pollutant gases


Pollutant gases


The Bhopal disaster

In 1984, Bhopal, India, a leak from a Union Carbide chemical plant killed and injured thousands.

Union Carbide paid nearly $500 million in compensation.

In 2001, Dow Chemical purchased Union Carbide. Dow claim that the compensation already paid by Union Carbide fulfils their responsibility. Many disagree, as can be seen from this photograph of a Dow chemical effigy being burned in 2004.


What is green chemistry?


1. Using renewable resources

Using renewable resources is the first key point in green chemistry.

Which method of ethanol synthesis is greener and why?

Ethanol can be made by the reaction of ethene (derived from crude oil) and water. Alternatively, it can be made by fermentation of biomass.

Ethanol, C2H5OH, is often used as a solvent for chemical reactions. It is also a raw material in the synthesis of useful compounds such as pharmaceuticals and pesticides, and can be used as a fuel.


2. Alternatives to hazardous chemicals

Many reactions in the chemical industry use a solvent to dissolve the raw materials. Examples include hexane, ethanol, propanone and dichloromethane.

Some solvents can be flammable and toxic, so safer alternatives are being researched.

An example of a safer solvent is the use of liquid carbon dioxide in dry cleaning. This is an alternative to the solvent

1,1,2,2-tetrachloroethane, which is toxic and harmful.


3. Atom economy


4. Use catalysts when possible

Common industrial catalysts include iron, platinum, vanadium(V) oxide and nickel. Enzymes can also be used as catalysts in industrial processes.

Only a small amount of a catalyst is needed in a reaction, and it can be recycled and reused multiple times.

Catalysts act by providing an alternative route for a reaction with a lower activation energy. At any given temperature, more particles are likely to have enough energy to react when they collide.

timeen

erg

y

with catalyst

without catalyst


Ethanoic acid

Ethanoic acid is used in a wide range of industrial processes, including the synthesis of polymers and adhesives. The most common method of production has changed, as follows:

What are the advantages of the new method of synthesis?

Old method New method

Reaction

Temperature

Pressure

Catalyst

Oxidation of butane producing a mixture

of products separated by fraction distillation

CH3OH + CO CH3COOH

180–200 °C 150–200 °C

40–50 atmospheres 30–60 atmospheres

cobalt(II) ethanoate iridium


Enzyme or metal?


5. Use energy efficiently

Energy is used in the chemical industry for heating, separating and drying.

There is also the potential for using solar power for heating and for water purification.

What are the advantages and disadvantages of using microwaves or solar power for heating?

Heat is often produced by burning fossil fuels. However, some reactions can now be carried out using microwaves to generate the heat needed.


6. Reduce and recycle waste

Many chemical plants recycle unreacted starting materials. For example, nitrogen and hydrogen are recycled in the Haber process to make ammonia:

Some factories also capture and make use of reaction by-products. For example, carbon dioxide is produced as a by-product in the synthesis of many chemicals. Chemical manufacturers now capture the carbon dioxide and sell it to fizzy drinks’ manufacturers.

N2 + 3H2 2NH3


7. Reducing water use

The chemical industry uses a great deal of water for cooling, cleaning and as a solvent.

What is the impact of warm water being released into rivers and streams?

Rather than releasing this water into the environment, many companies now trap and recycle the water. This reduces water use and prevents warm or contaminated water from polluting water systems.


8. Reducing pollution

Many plastics and detergents cause environmental problems because they are non-biodegradable.

For example, plastic bags and other packaging materials can be made from poly(lactic acid), which is biodegradable.

New plastics and detergents are being developed that will degrade to non-harmful waste products.


Meet the scientist


Which is greener?



Global warming: true or false?


What are greenhouse gases?


Global warming


Global warming potential

The GWP of a gas is calculated using the following factors:

ability of the gas to absorb infra-red radiation.

lifetime of the gas in the atmosphere

molar mass of the gas

The global warming potential (GWP) is a measure of how much a given gas can contribute to global warming over a

given time period. It is measured relative to carbon dioxide, which is given a global warming potential of 1.

Not all greenhouse gases contribute to global warming to the same degree.


Greenhouse gases compared

The contribution of a greenhouse gas to global warming depends on its global warming potential (GWP) and the amount of that gas present in the atmosphere.

Greenhouse gas

Average % of atmosphere

GWP

After 20 years

After100 years

water vapour

carbon dioxide

methane

nitrogenmonoxide

1–4

0.038

0.0002

0.00003

1 1

72 25

289 298

– –


The local effects of climate change


Causes of climate change


Causes of climate change


How scientists can help

It is now widely accepted that human activity is causing an increase in the concentration of carbon dioxide in the atmosphere, and that this is leading to global warming.

What is the role of scientists in combating global warming?

Analysing the available evidence to find out the current extent of the problem and predict its future extent.

Investigating the viability of controversial solutions, such as carbon capture and storage (CCS).


The role of co-operation

Because climate change is a global problem, co-operation is needed to achieve a solution.

It is not just scientists who are responsible for judging the effect of climate change. In 2006, the government published the Stern report, which stated that global warming could have a massive economic cost. Investment made into low-emission technologies was deemed economically worthwhile.

International co-operation is also important. For example many countries signed up to the Kyoto protocol, which requires countries to reduce their greenhouse gas emissions by a certain amount in a certain time.


What do you think?



What are carbon footprints?

Carbon footprint is a measure of the impact of a person’s activities on the environment, in terms of

how much CO2 is produced by each activity.

What do you think are the units of carbon footprint?

Country Average carbon footprint

USA

Australia

UK

China

India

20

17

10

3

1

(tonnes of CO2 per person per year)


Carbon footprints


Reducing your carbon footprint


What is carbon neutral?

Carbon neutral describes any activity that produces no overall emissions of CO2.

There are two ways of working towards carbon neutrality:

reducing carbon emissions

carbon offsetting.

Carbon offsetting is the practice of balancing activities that emit CO2 with activities that absorb it; for example,

planting trees that take in CO2 as they grow.

Carbon offsetting is controversial because the act of planting trees in large numbers uses energy and emits CO2 even if the trees themselves absorb it.


What is carbon neutral?

In 2003, the Rolling Stones went on the first carbon neutral tour. They calculated the amount of CO2 that would be produced by transporting the band, by fans travelling to the gigs and by energy use at the venues.

Radiohead toured in the summer of 2008 using only reduction of emissions, not carbon offsetting. Do you think both of these methods are equally good?

To make up for the CO2 produced, they organized the planting of two new forests in Scotland with trees that would absorb the same amount of CO2.


Are biofuels carbon neutral?


Advantages of biofuels


Is hydrogen carbon neutral?

When hydrogen is burned as a fuel, the only product is water.

Do you think hydrogen is a carbon neutral fuel?

The hydrogen fuel is generated by the electrolysis of water.

2H2 + O2 2H2O

Fuel cells that use this method of energy production can be incorporated into engines, as shown on the right.



What are CFCs?

Chlorofluorocarbons (CFCs), are a family of organic compounds.

dichlorodifluoromethane1,1,1–trichloro–

2,2,2–trifluoroethane

In the 1930s, CFCs were developed for use as refrigerants, to cool the air inside refrigerators.

They were then found to be useful in many other products, including aerosol sprays and foam fire extinguishers.

Two examples are:


What is the ozone layer?

The ozone layer is a high concentration of ozone (O3) molecules in a layer of the stratosphere about 15–30 km above the Earth’s surface.

Ozone absorbs a high proportion of the Sun’s ultraviolet radiation. There is strong evidence that this ultraviolet radiation is harmful.

What would be the impact of a lower concentration of ozone in the stratosphere?


CFCs and ozone

At ground level, CFCs are very stable. This is what allows them to exist in the atmosphere for long enough to reach the stratosphere. Once there, they absorb UV radiation from the Sun, which breaks their covalent bonds to form highly reactive free radicals.

These react very quickly with ozone molecules in a free radical chain reaction:

In this process, just one chlorine radical can destroy around 100 000 ozone molecules.

CCl2F2 ●CClF2 + Cl●

Cl● + O3 ClO● + O2 ClO● + O3 Cl● + 2O2


The Montreal protocol

The effect of CFCs on the ozone layer was established in the 1970s. In 1987 an international agreement called the Montreal protocol was put into place. It froze the production of CFCs and agreed to phase out their use from 1990.

Since CFCs are so stable, it will be many years before they disappear from the atmosphere. Some ozone depletion has therefore continued since the phasing out of CFCs.


CFCs and ozone: true or false



Glossary


What’s the keyword?


Multiple-choice quiz

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1 of 47© Boardworks Ltd 2009. 2 of 47© Boardworks Ltd 2009