This how it works covers Why Fractional Distillation Works within Crude Oil for GCSE Chemistry. Topic 37: Crude Oil It is section 5 of 13 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
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Section 5 of 13
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20 questions
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⚙️ Why Fractional Distillation Works
The fractionating column works because different hydrocarbon molecules have different strengths of forces between molecules, and these forces determine boiling points.
- Large molecules (long carbon chains) have stronger forces between molecules because they have more electrons. More energy is needed to separate them, so they have higher boiling points and condense low in the column where it is hotter.
- Small molecules (short carbon chains) have weaker forces between molecules. They need less energy to separate, so they have lower boiling points and rise higher up the column before condensing.
- The column has a continuous temperature gradient — hottest at the bottom (near 350°C) and coolest at the top (near 25°C). Each fraction condenses at the height where the temperature matches its boiling point.
- This is a physical separation — the hydrocarbon molecules themselves are not chemically changed. No bonds are broken or formed in the fractions.