AQA · Chemistry · 8462
GCSE Chemistry (AQA): Alkanes - Properties & Combustion
Topic 7 — Organic Chemistry. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Alkanes - Properties & Combustion (2027/28 exams)"; each card deep-links to the moment in the video it came from. Lesson 7.05 of Cognito's AQA GCSE Combined Science (Trilogy) and Chemistry course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-c_7.05.
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What is the balanced equation for the complete combustion of propane?
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C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
What does it mean for an alkane to be volatile?
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It evaporates easily. Shorter alkanes are more volatile because of their low boiling points.
What two products are formed by the complete combustion of a hydrocarbon?
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Carbon dioxide and water.
Combustion releases energy to the surroundings, so it is an ? reaction.
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exothermic
Why do the shortest hydrocarbons make the best fuels?
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They have the lowest boiling points, so they are the most volatile and the most flammable.
As alkane chain length increases, the liquid becomes more ?, meaning thicker and stickier.
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viscous
What is the state at room temperature of alkanes with 1–4 carbon atoms?
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Gases, because their short chains give them very low boiling points.
How does the boiling point of alkanes change as the carbon chain gets longer?
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It increases — longer chains have higher boiling points.
What condition is required for complete combustion of a hydrocarbon?
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A plentiful supply of oxygen.
Are shorter or longer alkanes more flammable?
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Shorter alkanes — they are easier to ignite, which makes them good fuels.
In combustion, what happens to the carbon and hydrogen in a hydrocarbon?
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They are oxidised — each combines with oxygen to form CO₂ and H₂O respectively.
What is the balanced equation for the complete combustion of nonane (C₉H₂₀)?
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C₉H₂₀ + 14O₂ → 9CO₂ + 10H₂O
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