C9 | chemistry of the atmosphere

Question 1

describe the proportions of gases in the modern atmosphere

Answer 1

• 78% of nitrogen
• 21% of oxygen
• small quantities of CO₂, H₂O and noble gases

Question 2

describe the earth’s early atmosphere and how it was formed

Answer 2

• the earth was hot when it was formed
• there was significant volcanic activity
• gases have been released from these volcanoes
• these gases included CO₂, N₂, CH₄, NH₃ and H₂O

Question 3

how did the amount of oxygen in the atmosphere increase?

Answer 3

• algae and plants produced the atmospheric O₂ by photosynthesis which can be represented by the equation:
  6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
• as the amount of O₂ gradually increased, there were more plants that produced oxygen

Question 4

how did the amount of carbon dioxide in the atmosphere decrease?

Answer 4

• some CO₂ was dissolved in the oceans, where it reacted with metal ions to form insoluble carbonates, such as CaCO₃, or was taken in by animals to become a part of a skeleton
• when an animal dies, this becomes a sedimentary rock
• some CO₂ was used in photosynthesis to make oxygen

Question 5

what is the greenhouse effect?

Answer 5

the increase in the temperature of the earth’s atmosphere due to the greenhouse gases in the atmosphere trapping infra-red radiation from the surface

Question 6

what are greenhouse gases?

Answer 6

• they are in the atmosphere
• they maintain temperatures on earth high enough to support life

Question 7

examples of greenhouse gases

Answer 7

• carbon dioxide
• methane
• water vapour

Question 8

why is the greenhouse effect necessary for life?

Answer 8

• the greenhouse effect is a natural phenomenon
• without it, the earth would be too cold for life to exist

Question 9

how have human activities led to an increase in greenhouse gases?

Answer 9

• carbon dioxide - combustion and deforestation
• methane - increased farming and decomposition in landfills

Question 10

what are the potential effects of global climate change?

Answer 10

• sea levels rise, which may cause flooding and increased coastal erosion
• more frequent and severe storms
• changes to the distribution of wildlife species

Question 11

what is a carbon footprint?

Answer 11

the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a production, service or event

Question 12

what actions can be taken to reduce a carbon footprint?

Answer 12

• increased use of alternative energy supplies
• energy conservation
• carbon capture and storage (where CO₂ is trapped in solvents and stored underground)

Question 13

what are the challenges faced with reducing a carbon footprint?

Answer 13

• scientific disagreement over causes and consequences of global climate challenge
• lack of public information and education
• lifestyle changes (people don’t want to give up their cars)

Question 14

what are the advantages of complete combustion?

Answer 14

• less carbon particulates produced
• more heat per gram of fuel is released
• poisonous carbon monoxide is not produced

Question 15

how is pollution caused by combustion?

Answer 15

• when a fuel burns, the gases released to the environment include carbon dioxide, water (vapour), carbon monoxide, sulphur dioxide and oxides of nitrogen
• solid particles and unturned hydrocarbons may also be released that form particulates in the atmosphere

Question 16

what are the issues regarding sulfur dioxide and oxides of nitrogen?

Answer 16

• they can cause respiratory problems in humans and cause acid rain
• acid rain damages plants and buildings

Question 17

what problems do particulates cause?

Answer 17

• particulates, such as carbon particles, called global dimming by reducing the amount of sunlight that reaches the earth’s surface
• particulates cause health problems for humans because of damage to the lungs

Question 18

acid rain

Answer 18

rain that is acidic due to dissolved gases, such as sulfur dioxide, produced from the burning of fossil fuels

Question 19

fossil fuels

Answer 19

natural fuels such as coal and gas formed in the past from the remains of living organisms

Question 20

global dimming

Answer 20

• a gradual reduction in the amount of light reaching the earth’s surface
• this can be caused by carbon particulates

Question 21

how do greenhouse gases trap energy from the sun?

Answer 21

long wavelength radiation is reflected back to the surface

Question 22

how do greenhouse gases keep the earth warm?

Answer 22

• allows shorter wavelength radiation to pass
• this is re-emitted as longer wavelength radiation
• this is absorbed by methane in the atmosphere

Question 23

which gas in the earth’s atmosphere is used when hydrocarbons burn?

Answer 23

oxygen

Question 24

why is it difficult to produce models for future climate change?

Answer 24

many different theories

Question 25

how does carbon dioxide help maintain temperatures on earth?

Answer 25

• carbon dioxide allows short wavelength radiation to pass through the atmosphere to the earth’s surface
• carbon dioxide absorbs outgoing long wavelength radiation

Question 26

when does incomplete combustion happen?
what does it produce?

Answer 26

• lack of oxygen
• it produces carbon

Question 27

why is soot formed when some fossil fuels are burned?

Answer 27

incomplete combustion - due to insufficient oxygen

Question 28

explain how reducing the amount of sulfur in fossil fuels reduces the erosion of limestone

Answer 28

• sulfur reacts with oxygen to form sulphur dioxide
• less sulfur dioxide is emitted
• less acid rain
• less limestone reacts with acid rain

Question 29

explain why oxides of nitrogen are formed in car engines

Answer 29

• car engines work at high temperatures
• in the engine, nitrogen reacts with oxygen

Question 30

how does carbon dioxide cause global warming?

Answer 30

• energy from the sun warms the earth’s surface
• infra-red radiation from the earth’s surface is trapped by carbon dioxide
• causing an increase in temperature