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Chemistry of the Atmosphere

AQA 2016 Chemistry topic 9

9.1 The Composition and Evolution of the Atmosphere

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26/03/2020The Earth’s Atmosphere

Carbon dioxide, water vapour Oxygen Nitrogen Noble gases

For the last 200 million years the atmosphere has remained roughly the same – it contains 78% nitrogen, 21% oxygen, 1% noble gases and about 0.03% CO2

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4 Billion years 3 Billion years 2 Billion years 1 Billion years Present day

Evolution of the Earth’s AtmosphereCarbon

dioxide

Methane Ammonia Oxygen Nitrogen Others

The early atmosphere was like the present-day atmosphere of Venus or Mars

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4 Billion years 3 Billion years 2 Billion years 1 Billion years Present day

Evolution of the Earth’s AtmosphereVolcanic activity releases nitrogen, CO2, methane, ammonia and water vapour into the atmosphere. The water vapour condenses to form oceans.

Evidence for the early atmosphere is limited. Why is that?

Carbon from CO2 becomes locked up in sedimentary rocks as carbonates and fossil fuels. As the oceans form by condensing water vapour the carbonates and fossil fuels become locked underground, decreasing the amount of CO2.

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Changes in Oxygen and CO226/03/2020

4 Billion years 3 Billion years 2 Billion years 1 Billion years Present day

Carbon dioxide + water glucose + oxygen

6CO2 + 6H20 C6H12O6 + 6O2

Sunlight

Chlorophyll

Sunlight

Chlorophyll

Q. What are the equations for photosynthesis?

Somewhere around 2.7 billion years ago, algae and plants arrived and started taking in carbon dioxide and producing oxygen. A billion years later, there was enough oxygen for animals to evolve.

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Decreasing Carbon DioxideAs well as photosynthesis by plants and algae, atmospheric carbon dioxide levels were also decreased by the formation of carbonate rocks, e.g.:

ChalkLimestone

Marble (made from chalk or limestone)

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Formation of oil and gas

1) Layers of dead sea _____ settle on the seabed.

2) Layers of __________ rock build up on top.

3) The heat and ________ from these rocks, along with the absence of ______, mean that oil and gas are formed over ______ of years.

Words – sedimentary, millions, oxygen, creatures, pressure

9.2 Carbon Dioxide and Methane as Greenhouse Gases

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26/03/2020Carbon Dioxide and Global Warming

Global levels of Carbon Dioxide in PPM

Is there a link?

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The Greenhouse Effect1) Heat and light energy reach us from the sun (higher wavelengths such as visible light)…

2) …a lot of this heat is reflected off the Earth’s surface as lower wavelength infra red…

3) …some of the heat escapes back into space…

4) …while some of it is reflected back to the Earth by a layer of greenhouse gases (water vapour, CO2

and methane) – this is called The Greenhouse Effect

What problems do these next pictures show?

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26/03/2020Humans Causing Greenhouse Gases

How do the following activities affect the amount of greenhouse gases in the atmosphere?

1) Excessive burning of fossil fuels…

2)Large scale deforestation…

3) Large scale cattle farming

26/03/2020Carbon Dioxide and Global Warming

Global levels of Carbon Dioxide in PPM

Many scientists believe that

human activities will cause global

warming.

What reasons would people have for believing this?

What reasons would stop people believing global warming is happening?

Effects of Global Climate Change26/03/2020

What possible effects of climate change do these pictures show?

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Carbon Footprint26/03/2020

The “carbon footprint” is defined as the total amount of carbon dioxide and other greenhouse gases emitted over the full cycle of a product or event.

1) Drill for crude oil2) Put the oil through fractional

distillation3) Crack alkanes to make ethene4) Use heat to polymerise ethene5) Transport plastic bags to shops6) Transport bags to landfill sites

Steps in the bag’s life cycle

1) Use recycled materials2) Reduce consumption of the bags3) Manufacture them closer to

shops4) Recycle the bags after use

Ways to reduce the footprint

Q. Consider the humble plastic bag. What steps are involved in its life cycle and how can the carbon footprint of each step be reduced?

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Other ways to reduce the footprintHere are some other ways to reduce the carbon footprint:

Offset with renewable energy

Increase recycling

Personal choice

Carbon capture

Use better insulation

What factors might limit these options?

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9.3 Common Atmospheric Pollutants and their Sources

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PollutionSome examples of pollution…

Carbon dioxide, water vapour, carbon monoxide are caused by the burning of ____ _____. Carbon monoxide is a ____ gas and is not easily detected due to being ________.

Sulfur dioxide and nitrogen dioxide cause ____ ____ which damages trees and buildings and _________ problems in humans.

Particulates (unburned _______) can make buildings dirty and worsen breathing difficulties and cause global ______.

Words – hydrocarbons, dimming, fossil fuels, odourless, acid rain, respiratory, toxic

26/03/2020Combustion of Fuels

Lots of oxygen:

Some oxygen:

C

H

H

H

HO

O

OO

OH H

OH H

CO

O

Methane Oxygen+ Water+Carbon dioxide

Oxygen+

OO

OO

OO

Methane

C

H

H

H

H

C

H

H

H

H

Carbon monoxide

CO

CO

Water+

OH H

OH H

OH H

OH H

26/03/2020Other products of burning fuelsSulphur dioxide:

Nitrogen monoxide:

Nitrogen dioxide:

SO

O

Sulphur dioxide

SO

O

Sulphur Oxygen+

Nitrogen monoxide

NO

NO

Oxygen+

OO

Nitrogen

NN

OO

Oxygen+Nitrogen monoxide

NO

NO

Nitrogen dioxide

N OO

N OO

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Incomplete CombustionAs well as producing carbon monoxide, incomplete combustion can also produce soot:

Little oxygen:

CC

H

H

H

H

Methane

OO

Oxygen+

OH H

OH H

Water+Carbon

“Soot”

• 4 marks

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