Greenhouse Gases
Master Greenhouse Gases for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Greenhouse gases such as carbon dioxide, methane and water vapour absorb re-radiated heat, keeping the Earth warm.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Greenhouse gases in the atmosphere maintain temperatures on Earth high enough to support life. The main ones are water vapour, carbon dioxide and methane.
The mechanism has three stages. Short wavelength radiation from the Sun passes through the atmosphere and is absorbed by the Earth's surface. The Earth then radiates energy back out at longer wavelengths, as infrared. Greenhouse gases absorb this outgoing long wavelength radiation and re-radiate some of it back towards the Earth.
The result is that energy is retained rather than escaping into space, keeping the Earth warm. Without greenhouse gases the Earth would be far too cold to support life, so the effect itself is essential — the problem is the increase in concentration.
Revision notes
The main greenhouse gases
Water vapour, carbon dioxide and methane.
They absorb long wavelength radiation and are present in small proportions, but their effect on temperature is substantial.
The mechanism
Short wavelength radiation from the Sun passes through the atmosphere and is absorbed by the Earth's surface.
The Earth radiates energy back at longer wavelengths, as infrared. Greenhouse gases absorb this and re-radiate some back towards the Earth, so energy is retained rather than escaping.
Why it matters
The greenhouse effect is essential — without it the Earth would be too cold to support life.
The concern is the increase in the concentration of greenhouse gases from human activity, which retains more energy and raises average global temperature.
Key points
- Water vapour, carbon dioxide and methane are greenhouse gases.
- Short wavelength radiation passes through the atmosphere.
- The Earth radiates energy at longer wavelengths.
- Greenhouse gases absorb the long wavelength radiation.
- Some energy is re-radiated back towards Earth.
- The greenhouse effect is essential for life.
Worked examples
Example 1
Name three greenhouse gases. [3 marks]
Model answer
Water vapour (1 mark), carbon dioxide (1 mark) and methane (1 mark).
Example 2
Explain how greenhouse gases keep the Earth warm. [3 marks]
Model answer
Short wavelength radiation from the Sun passes through the atmosphere and is absorbed by the Earth's surface (1 mark). The Earth radiates energy back at longer wavelengths (1 mark). Greenhouse gases absorb this long wavelength radiation and re-radiate some of it back towards the Earth, so energy is retained (1 mark).
Example 3
Explain why the greenhouse effect is necessary for life on Earth. [2 marks]
Model answer
It retains energy that would otherwise escape into space (1 mark), keeping the Earth's temperature high enough for living organisms to survive (1 mark).
Common mistakes
Saying greenhouse gases reflect radiation.
They absorb it and re-radiate some back — a different mechanism.
Saying the greenhouse effect is entirely harmful.
It is essential for life; the problem is the increasing concentration.
Not distinguishing the wavelengths.
Incoming radiation is short wavelength; outgoing is long wavelength.
Naming oxygen as a greenhouse gas.
The main ones are water vapour, carbon dioxide and methane.
Exam tips
- Learn the three-stage mechanism in order.
- Distinguish short and long wavelength radiation.
- Say absorbed and re-radiated, not reflected.
- State that the effect itself is essential.
Key terms
- Greenhouse gas
- A gas absorbing long wavelength radiation from the Earth.
- Greenhouse effect
- The retention of energy by gases in the atmosphere.
- Long wavelength radiation
- Infrared radiation emitted by the Earth.
- Re-radiate
- To emit absorbed energy again.
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Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.