GCSE Chemistry: The Atmosphere (T9)

Describe the proportion of the gases in the atmosphere of the Earth today.

(stayed much the same for past 200 million years)

• 78% nitrogen

• 21% oxygen

• there are also small proportions of other gases e.g.

  • carbon dioxide-0.04%

  • water vapour

  • noble gases

Describe theories about what was in the Earth’s early atmosphere.

• One theory suggests that during the first billion years of the Earth’s existence there was intense volcanic activity that released gases that formed the early atmosphere and water vapour that condensed to form the oceans.

• Volcanoes also released huge amounts of carbon dioxide so at the start of this period the Earth’s atmosphere may have been like the atmospheres of Mars and Venus today, consisting of mainly carbon dioxide with little or no oxygen gas.

• Volcanoes also produced nitrogen which gradually built up in the atmosphere and there may have been small proportions of methane and ammonia.

How did carbon dioxide decrease in the atmosphere?

• Algae and plants decreased the percentage of carbon dioxide in the atmosphere by photosynthesis.

• Carbon dioxide was also decreased by the formation of sedimentary rocks and fossil fuels that contain carbon.

How did oxygen increase in the atmosphere?

• Around 2.7 billion years ago, photosynthetic algae first evolved in the oceans

• Photosynthesis produced oxygen which entered the atmosphere.

• Over the following billion years, plants evolved, increasing the amount of oxygen in the atmosphere

• As well as producing oxygen, photosynthesis also takes in carbon dioxide

Describe the formation of limestone.

• When the water vapour from volcanoes condensed to form the oceans, some of the carbon dioxide dissolved in the oceans to form a weak acid .

• This reacted with minerals in the sea to form precipitates and over time this formed sediments of carbonate rocks on the sea bed

• Corals and shells of organisms such as mussels are full of calcium carbonate.

• When these died, they formed the sedimentary rock limestone.

How long does it take for fossil fuels to form?

Millions of years

Formation of gas

• natural gas is mainly the hydrocarbon methane → often find in near deposits of oil

• Natural gas → formed from plankton - similar way to oil

• All fossil fuels contain trapped carbon→that carbon was part of the carbon dioxide taken in by photosynthesis

• Chemical reaction	Hâ‚‚, COâ‚‚, Oâ‚‚, SOâ‚‚, etc.
  Boiling or evaporation	Water vapour
  Respiration or decay	CO₂, CH₄, NH₃
  Thermal decomposition	COâ‚‚

Are fossil fuels renewable or non-renewable?

non-renewable

Describe the formation of coal

• Coal is formed from the remains of ferns and trees

• If these die in marshy wetlands then they do not decompose.

• (That can be due to a lack of oxygen or acidic conditions- these both prevent bacteria from carrying out decomposition.)

• Over time the plant remains are covered with sediments and compressed

• High temperature and pressure creates coal.

Describe the formation of crude oil.

• Crude oil is formed from plankton, which are tiny plants and animals found in the sea.

• When these die they settle in mud on the sea-bed.

• (If oxygen is not present then they do not decompose)

• Over time, they are compressed by sediment and heat and pressure then convert them into crude oil.

Where is natural gas often found?

Near deposits of oil because natural gas is formed from plankton is a similar way to oil

What do greenhouse gases do in the atmosphere?

• Energy from the sun travels to the Earth as short wavelength radiation e.g. ultraviolet and visible light

• (Some of the short wavelength radiation simply reflects back into space but most of it passes easily through the atmosphere because short wavelength radiation does not interact strongly with the gas molecules in the atmosphere)

• The energy of the radiation is absorbed when it reaches the surface of the earth.

• The surface of the Earth now radiates the energy as long wavelength radiation such as infra-red.

• Some of the long wavelength radiation interacts with the greenhouse gas molecules in the atmosphere- the energy in the long wavelength radiation is absorbed.

• Because the energy is trapped in the atmosphere, this causes the temperature of the atmosphere to increase.

Significance of greenhouse effect

• Keeps the temperature on Earth warm enough to support life. Without the greenhouse effect the Earth would be too cold for most living organisms to survive.

What are the main greenhouse gases?

• Carbon dioxide

• Methane

• Water vapour

Why does the level of water vapour in the atmosphere vary widely?

Because it depends on the temperature of the air.

Why are the levels of carbon dioxide and methane increasing?

Because of human activity.

Reasons for increase in CO2

• Burning fossil fuels releases CO2

• Petrol and diesel to power vehicles release CO2

• Gas to heat buildings release CO2

• Growing trees in rainforests absorb CO2 and because of deforestation of rainforests more trees release CO2 back into the atmosphere.

Reasons for increase in methane

• Released in agriculture e.g. growing rice in flooded paddy fields

• Released when cattle such as cows pass wind.

Possible effects of climate change

• Flooding- Rising temperatures will increase melting of the polar ice sheets and glaciers. This will lead to increased sea levels. This could lead to more flooding of low-lying areas.

• Could lead to more severe weather e.g. storms

• Increasing temperatures could change the distribution of animals in a habitat.

What do many scientists believe causes climate change?

Based on peer-reviewed evidence, many scientists believe that human activities will cause the temperature of the Earth’s atmosphere to increase at the surface and that this will result in global climate change.

Why are there problems with our understanding of climate change?

Because climate change is complex and difficult to model. This leads to simplified models, speculation and opinions presented in the media that may be based on only parts of the evidence and which may be biased.

What does carbon footprint mean?

The carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.

• The carbon footprint can be reduced by reducing emissions of carbon dioxide and methane

How can carbon footprint be reduced?

• By insulating our homes (or turning down the heating) so we spend less energy heating our homes. As fossil fuels such as gas are commonly used to heat homes, insulating homes (or turning down the heating) will reduce the use of gas thus reducing CO2 emissions/carbon footprint.

• Lots of CO2 is released by driving cars- this can be reduced through the increased use of public transport such as trains and buses as it releases less CO2 per passenger.

• Lots of CO2 is produced by generating electricity by burning fossil fuels- this can be reduced through the use of other sources of energy that don’t emit CO2 e.g. wind power. One can also reduce how much electricity they use at home (can use energy-saving lightbulbs, turn appliances off at the plug).

• Cattle release methane- reducing the consumption of beef and dairy products reduce carbon footprint as less methane is being released into the atmosphere.

• Methane is also emitted in landfills- this can be reduced by trapping the methane and burning it to produce electricity. (Methane is also a more power greenhouse gas than CO2 so less will be needed). However trapping and burning methane is expensive.

Why may these actions of reducing carbon footprint be limited?

• Most of these solutions are expensive and people are reluctant to pay

• In some cases they’re inconvenient

• People enjoy eating beef and dairy products and may be unwilling to change it.

Describe pollutants from fuels

• The combustion of fuels is a major source of atmospheric pollutants.

• Most fuels contain carbon and hydrogen and may also contain some sulfur. When these fuels are burned/combusted the carbon and hydrogen atoms react with oxygen in the air. (oxidised)

• The gases released into the atmosphere may include carbon ,carbon dioxide, water vapour, carbon monoxide sulfur dioxide and oxides or nitrogen.. Solid particles and unburned hydrocarbons may also be released that form particulates in the atmosphere

• Carbon dioxide is a greenhouse gas the emition of it contributes to climate change.

• Carbon monoxide is a toxic, colourless and odourless gas. (To protect themselves many have CO detectors).

• Sulfur dioxide and oxides of nitrogen cause breathing problems in humans. They also dissolve in rainwater to form acid rain. Acid rain can damage trees and corrode buildings made from limestone.

• Clouds of black particles are produced by engines. These are particles of carbon (soot) and unburned hydrocarbons. Scientists call this type of pollution particulates. Particulates can damage human health e.g. they increase the rate of heart and lung disease. They can also reduce the amount of energy from the sun that reaches the Earth’s surface (global dimming).

Describe the production of CO2 CO SO2 and oxides of nitrogen

• CO2 is produced during complete combustion when there’s enough oxygen.

• CO and C are produced are produced during incomplete combustion due to the lack of oxygen for the oxidisation reaction.

• Sulfur dioxide is produced when fuels ( that contain sulfur) are burned because the sulfur atoms oxidise to produce sulfur dioxide.

• Oxides of nitrogen are produced inside engines. Here high temperatures cause nitrogen and oxygen from the air to react. This produces a range of different molecules so scientists call them all oxides of nitrogen (NOx).