Greenhouse gases — AQA GCSE Chemistry
Test yourself on Greenhouse gases with AQA GCSE practice questions.
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Greenhouse gases explained
The greenhouse effect depends on how radiation of different wavelengths interacts with matter.
Read the full explanation
Short wavelength radiation from the Sun, mainly visible and ultraviolet, passes through the atmosphere and is absorbed by Earth's surface, warming it. The warmed surface emits longer wavelength infrared radiation. Greenhouse gas molecules in the atmosphere absorb this infrared radiation because their bonds can vibrate at frequencies matching that energy. The absorbed energy is re-emitted in all directions, including back to Earth, so less escapes to space and the surface stays warmer. This is a continuous energy balance: incoming short wavelength radiation, outgoing long wavelength radiation, and absorption and re-emission by greenhouse gases.
Your focus
- Describe the greenhouse effect using short and long wavelength radiation.
- Explain how greenhouse gases absorb and re-emit infrared radiation.
- Relate the greenhouse effect to the balance of incoming and outgoing energy.
Greenhouse gases exam tips
Marking Points
- Short wavelength radiation from the Sun, including visible and ultraviolet, passes through the atmosphere and is absorbed by Earth's surface.
- Earth's warmed surface emits longer wavelength infrared radiation.
- Greenhouse gas molecules absorb infrared radiation and re-emit it in all directions, including back towards Earth.
- Because some infrared energy is returned, less energy escapes to space and surface temperature is maintained.
- The interaction depends on wavelength: short wavelength radiation is largely transmitted, while long wavelength infrared is absorbed by greenhouse gases.
- The process is a balance between incoming solar energy and outgoing infrared energy.
Examiner Tips
- 💡Use the terms 'short wavelength' for incoming solar radiation and 'long wavelength' or 'infrared' for radiation emitted by Earth.
- 💡Explain the sequence: Sun emits short wavelength, Earth absorbs and warms, Earth emits infrared, greenhouse gases absorb and re-emit.
- 💡Avoid saying heat is 'trapped' without explaining absorption and re-emission, as this shows the mechanism more clearly.
Common Mistakes
- Saying greenhouse gases reflect infrared radiation; they absorb and re-emit it, which is different from reflection.
- Claiming short wavelength radiation is trapped by greenhouse gases; it is mainly the longer wavelength infrared emitted by Earth that is absorbed.
- Describing the greenhouse effect as a one-way trapping process; energy is continuously absorbed, re-emitted and partly lost to space.