Sources of carbon dioxide and methane
Trace carbon dioxide to combustion, respiration and carbonate reactions, then identify methane in natural gas and compare their climate role.
Section C10.3 · Carbon dioxide and methane
An original 0652 lesson joining the listed gas sources to existing air and fuel teaching. Written practice is self-checked and does not predict an official grade.
Before you begin
- Recognise carbon-containing fuels
- Read simple word and symbol equations
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which two gases are identified as greenhouse gases in this section?
What you will learn
- Identify the listed sources of carbon dioxide
- Name methane as the main constituent of natural gas
- Recognise carbon dioxide and methane as greenhouse gases
Where carbon dioxide forms
Carbon dioxide forms during the complete combustion of carbon-containing substances and during respiration. It also forms when acids react with carbonates and when calcium carbonate thermally decomposes.
A simplified respiration equation is glucose + oxygen → carbon dioxide + water. A complete-combustion equation for methane is CH₄ + 2O₂ → CO₂ + 2H₂O.
Methane and natural gas
Methane is the main constituent of natural gas. Coal, natural gas and petroleum are fossil fuels; burning them produces carbon dioxide. Carbon dioxide and methane are greenhouse gases because they absorb infrared radiation in the atmosphere.
Keep source and effect separate
A sound explanation distinguishes how a gas is formed from what it does in the atmosphere. For example, methane can be released from a fuel source, while its greenhouse-gas role describes how it affects outgoing infrared energy.
Sources for this lesson
Pause and explain
Which statement about methane and natural gas is correct?
Worked example
Name the main gas in natural gas and give one chemical process that forms carbon dioxide.
Show the worked solution
- Natural gas is mainly methane.
- Carbon dioxide can form in complete combustion, respiration, or a carbonate reaction.
- Give one distinct example rather than treating the two gases as the same substance.
Answer Methane is the main constituent of natural gas. One process that forms carbon dioxide is the complete combustion of a carbon-containing fuel, such as methane.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Complete the word equation for aerobic respiration and identify the carbon-containing gas formed.
Give me a hint
Glucose reacts with oxygen; the products include water and a carbon oxide.
Compare my reasoning
- Write glucose and oxygen as the reactants.
- Respiration produces water and carbon dioxide.
- Check that carbon appears in the carbon dioxide product.
Glucose + oxygen → carbon dioxide + water. The carbon-containing gas formed is carbon dioxide.
Look for these in your work
- Names glucose and oxygen as reactants
- Includes carbon dioxide and water as products
- Identifies carbon dioxide
Write a balanced equation for complete combustion of methane and identify the greenhouse gas in the products.
Give me a hint
One methane molecule contains one carbon; balance hydrogen and then oxygen.
Compare my reasoning
- Write CH₄ + O₂ → CO₂ + H₂O.
- Four hydrogen atoms require two water molecules.
- The products then contain four oxygen atoms, so use two oxygen molecules.
CH₄ + 2O₂ → CO₂ + 2H₂O. Carbon dioxide is a greenhouse gas; methane is also a greenhouse gas before it reacts.
Look for these in your work
- Balances hydrogen
- Balances oxygen
- Identifies carbon dioxide correctly
A student says methane and carbon dioxide are the same because both are greenhouse gases. Correct the statement and use the natural-gas fact.
Give me a hint
Give each gas a different formula or role.
Compare my reasoning
- Name methane as CH₄ and carbon dioxide as CO₂.
- State that methane is the main constituent of natural gas.
- Explain that sharing a greenhouse-gas category does not make two substances identical.
Methane (CH₄) and carbon dioxide (CO₂) are different compounds, although both are greenhouse gases. Methane is the main constituent of natural gas; carbon dioxide forms from processes such as respiration and complete combustion.
Look for these in your work
- Distinguishes the formulas
- States the natural-gas relationship
- Keeps gas identity separate from greenhouse effect
Common mistakes
- Do not call natural gas pure methane; methane is its main constituent.
- Do not confuse carbon dioxide and methane: both are greenhouse gases, but they are different compounds.
- Do not state that every combustion reaction is complete; the syllabus source is complete combustion.
What can you explain now?
Which gas is the main constituent of natural gas?
Compare with the explanation
Methane.
Methane is the principal component specified for natural gas in the syllabus.
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Make it stick
Recall three listed ways carbon dioxide forms and name the main constituent of natural gas.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.