Carbon dioxide and methane
Cambridge IGCSE Chemistry (0620) · Unit 10: Chemistry of the environment · 13 flashcards
Carbon dioxide and methane is topic 10.3 in the Cambridge IGCSE Chemistry (0620) syllabus , positioned in Unit 10 — Chemistry of the environment , alongside Water and Air and air quality. In one line: Clean, dry air is approximately 78% nitrogen (N₂), 21% oxygen (O₂), and about 1% argon (Ar). Carbon dioxide (CO₂) is a trace gas, typically around 0.04% (400 ppm). These proportions are vital for understanding atmospheric chemistry and the greenhouse effect.
This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical).
The deck below contains 13 flashcards — 3 definitions, 6 key concepts and 4 identification cards — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.
The approximate composition of clean, dry air
Clean, dry air is approximately 78% nitrogen (N₂), 21% oxygen (O₂), and about 1% argon (Ar). Carbon dioxide (CO₂) is a trace gas, typically around 0.04% (400 ppm). These proportions are vital for understanding atmospheric chemistry and the greenhouse effect.
What the Cambridge 0620 syllabus says
2026-2028 syllabus, in our wordsWhat the syllabus expects you to be able to do in this topic, in plain English. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks. For the exact wording, see the official syllabus (PDF).
- State State that clean, dry air is roughly 78% nitrogen, N₂, and 21% oxygen, O₂, with the rest made up of a mixture of carbon dioxide, CO₂, and noble gases.
- State State where each of these air pollutants comes from (only these): carbon dioxide, from complete combustion of fuels containing carbon; carbon monoxide and particulates, from incomplete combustion of fuels containing carbon; methane, from rotting vegetation and from waste gases made during digestion in animals; oxides of nitrogen, from car engines; sulfur dioxide, from burning fossil fuels that contain sulfur compounds.
- State State the harmful effect of each pollutant (only these): carbon dioxide and methane, where raised levels increase global warming, which causes climate change; carbon monoxide, a toxic gas; particulates, a greater risk of cancer and of respiratory problems; oxides of nitrogen, photochemical smog, acid rain and respiratory problems; sulfur dioxide, acid rain.
- Describe Describe how carbon dioxide and methane, as greenhouse gases, lead to global warming, using only these ideas: thermal energy being absorbed, reflected and emitted; and less thermal energy escaping into space. Supplement
- State State and explain ways of lessening these environmental problems (only these): for climate change, planting trees, keeping fewer livestock, burning less fossil fuel, and using more hydrogen and renewable energy such as wind and solar; for acid rain, fitting catalytic converters to vehicles, and cutting sulfur dioxide emissions by using low-sulfur fuels and by desulfurisation of flue gases using calcium oxide.
- Describe Describe photosynthesis as a reaction in which carbon dioxide and water form glucose and oxygen, using energy from light, with chlorophyll present.
- State State, as a word equation, how carbon dioxide and water react in photosynthesis to give glucose and oxygen: carbon dioxide + water → glucose + oxygen.
- Explain Explain how nitrogen oxides are produced inside car engines, and describe how a catalytic converter removes them, e.g. 2CO + 2NO → 2CO₂ + N₂. Supplement
- State State the balanced symbol equation for photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Supplement
What two reactants are required for photosynthesis?
Photosynthesis requires carbon dioxide and water. Plants take in carbon dioxide from the atmosphere through their leaves and absorb water from the soil through their roots. In the presence of sunlight and chlorophyll, these reactants are converted into glucose and oxygen.
What is the approximate composition of clean, dry air?
Clean, dry air is approximately 78% nitrogen (N₂), 21% oxygen (O₂), and about 1% argon (Ar). Carbon dioxide (CO₂) is a trace gas, typically around 0.04% (400 ppm). These proportions are vital for understanding atmospheric chemistry and the greenhouse effect.
What is a major source of carbon dioxide air pollution?
Carbon dioxide (CO₂) is primarily produced from the complete combustion of carbon-containing fuels, such as burning wood, coal, and gasoline in power plants and vehicles.
What is a major source of methane air pollution?
Methane (CH₄) is released from the decomposition of vegetation, such as in wetlands and rice paddies. It is also released as a waste gas from digestion in animals, especially livestock like cows.
What is an adverse effect of increased carbon dioxide levels in the atmosphere?
Higher levels of carbon dioxide (CO₂) lead to increased global warming, which in turn causes climate change. This can result in rising sea levels, more frequent extreme weather events, and disruptions to ecosystems.
What is an adverse effect of increased methane levels in the atmosphere?
Higher levels of methane (CH₄) lead to increased global warming, which leads to climate change. Methane is a more potent greenhouse gas than carbon dioxide over a shorter timeframe.
How do carbon dioxide and methane cause global warming?
Carbon dioxide (CO₂) and methane (CH₄) absorb thermal energy (infrared radiation) emitted from the Earth's surface. They then re-emit some of this energy back towards the Earth, reducing thermal energy loss to space and warming the planet.
State a strategy to reduce the effects of climate change.
Strategies include planting trees (afforestation), reducing livestock farming to lower methane emissions, decreasing the use of fossil fuels, and increasing the use of hydrogen and renewable energy sources like wind and solar power.
Write the word equation for photosynthesis.
Carbon dioxide + water → glucose + oxygen. This reaction uses energy from light and chlorophyll.
State the symbol equation for photosynthesis.
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. This shows the chemical formulas and the balanced stoichiometry of the reaction.
Name two greenhouse gases.
Carbon dioxide (CO₂) and methane (CH₄) are greenhouse gases. Water vapour and nitrous oxide are also greenhouse gases.
What is the chemical formula for methane?
CH₄ (methane). This indicates one carbon atom and four hydrogen atoms.
What are the reactants of photosynthesis?
Carbon dioxide (CO₂) and water (H₂O) are the reactants of photosynthesis. These are converted into glucose and oxygen.
Key Questions: Carbon dioxide and methane
What is the approximate composition of clean, dry air?
Clean, dry air is approximately 78% nitrogen (N₂), 21% oxygen (O₂), and about 1% argon (Ar). Carbon dioxide (CO₂) is a trace gas, typically around 0.04% (400 ppm). These proportions are vital for understanding atmospheric chemistry and the greenhouse effect.
Write the word equation for photosynthesis.
Carbon dioxide + water → glucose + oxygen. This reaction uses energy from light and chlorophyll.
State the symbol equation for photosynthesis.
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. This shows the chemical formulas and the balanced stoichiometry of the reaction.
More topics in Unit 10 — Chemistry of the environment
Carbon dioxide and methane sits alongside these Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 0620 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Key terms covered in this Carbon dioxide and methane deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
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