Climate Change and Atmospheric Pollutants
Climate change and atmospheric pollutants cover the evidence linking human activity to climate change, the possible consequences of a rising global temperature, and the pollutants released into the atmosphere when fuels are burned. Complete combustion of a hydrocarbon fuel in plenty of oxygen produces only carbon dioxide and water, but incomplete combustion, in limited oxygen, also produces toxic carbon monoxide and solid carbon particulates; sulfur impurities in fuels form sulfur dioxide, and the heat of combustion itself can make nitrogen and oxygen from the air react to form nitrogen oxides, both of which contribute to acid rain.
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Method
- State the correlating evidence linking human activity to climate change: measurements of atmospheric carbon dioxide (from direct sampling and from air trapped in ice cores) show a rise since the industrial revolution, alongside a corresponding rise in average global temperature over the same period.
- List the possible consequences of climate change relevant at GCSE: rising sea levels (from thermal expansion of the oceans as they warm and from melting glaciers and ice sheets), changing rainfall and more frequent extreme weather events, and changes to the distribution of species and to growing seasons for crops.
- Distinguish complete from incomplete combustion of a hydrocarbon fuel by the amount of oxygen available: complete combustion, in plenty of oxygen, produces only carbon dioxide and water; incomplete combustion, where oxygen is limited, also produces carbon monoxide and/or solid carbon particulates (soot).
- Explain why carbon monoxide is dangerous: it is a colourless, odourless, toxic gas that binds to haemoglobin in red blood cells more readily than oxygen does, reducing the blood's ability to carry oxygen around the body, which can cause suffocation without warning.
- Explain the source of sulfur dioxide and nitrogen oxides: sulfur dioxide forms from sulfur impurities present in some fuels burning alongside the fuel; nitrogen oxides form when the high temperature inside an engine or furnace causes nitrogen and oxygen from the air itself to react, not from the fuel.
- Link sulfur dioxide and nitrogen oxides to acid rain and to particulates to two further problems: both gases dissolve in atmospheric water droplets to form acidic solutions that fall as acid rain, damaging buildings, trees and aquatic ecosystems; solid particulates cause global dimming, by reflecting sunlight back into space and providing surfaces on which clouds form, and both particulates and these gases cause respiratory problems in humans.
Worked example
Octane, C8H18, is a hydrocarbon fuel used in petrol. Write a balanced symbol equation for the complete combustion of octane, and explain why incomplete combustion, producing carbon monoxide, is more likely to happen inside a car engine than in an open Bunsen burner flame.
- Write the word equation for complete combustion: octane + oxygen gives carbon dioxide + water.
- Write the unbalanced symbol equation: C8H18 + O2 gives CO2 + H2O.
- Balance carbon and hydrogen first, since octane has 8 carbon atoms and 18 hydrogen atoms: C8H18 + O2 gives 8CO2 + 9H2O.
- Balance oxygen: the right side has (8 x 2) + 9 = 25 oxygen atoms, so 12.5 O2 molecules are needed; to avoid a fraction, double every term in the whole equation: 2C8H18 + 25O2 gives 16CO2 + 18H2O.
- Check the balance: 16 carbon, 36 hydrogen and 50 oxygen atoms appear on both sides, so the equation is balanced.
- Explain incomplete combustion in an engine: inside a car engine, fuel burns rapidly in a sealed, confined space where the air supply (and so the oxygen supply) is often insufficient for the amount of fuel burning, unlike an open Bunsen flame where a large, unrestricted supply of air is available, so an engine is more likely to produce carbon monoxide and soot from incomplete combustion.
Practice questions
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Q1State the two products of the complete combustion of a hydrocarbon fuel.Show answer
Answer: Carbon dioxide and water.
Q2Name the two additional products that can form during the incomplete combustion of a hydrocarbon fuel.Show answer
Answer: Carbon monoxide and solid carbon particulates (soot).
Q3Explain why carbon monoxide is dangerous even though it has no smell.Show answer
Answer: It is toxic because it binds to haemoglobin in red blood cells more strongly than oxygen does, which reduces the amount of oxygen the blood can carry around the body; because it is colourless and odourless, a person can be poisoned by it without noticing.
Q4Explain why burning a fuel can produce nitrogen oxides even if the fuel itself contains no nitrogen.Show answer
Answer: The high temperature produced by combustion can cause nitrogen and oxygen from the air itself to react together, forming nitrogen oxides; the nitrogen does not need to come from the fuel.
Q5Name two gases that dissolve in atmospheric water droplets to cause acid rain.Show answer
Answer: Sulfur dioxide and nitrogen oxides.
Q6Give one piece of evidence used to link human activity to recent climate change.Show answer
Answer: Measurements of atmospheric carbon dioxide concentration, from direct sampling and from air trapped in ice cores, show a rise since the industrial revolution that correlates with a rise in average global temperature over the same period.
Q7Explain how solid carbon particulates released by combustion can cause global dimming.Show answer
Answer: The particulates reflect sunlight back into space before it reaches the Earth's surface, and they can also encourage extra cloud formation, both of which reduce the amount of sunlight reaching the ground.
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
Explain the scientific evidence that links rising levels of carbon dioxide to climate change, and evaluate two possible consequences for the environment and for human populations if global temperatures continue to rise.
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A coal-fired power station burns coal that contains sulfur impurities. Explain, giving the source of each pollutant, how burning this coal contributes to acid rain, and describe one environmental effect of acid rain.
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Free printable worksheet
Want more practice on paper? Download the climate change and atmospheric pollutants worksheet pack - 18 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 29 of GCSE Chemistry Workbook, the whole course as one free printable PDF.
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