Bromoethane can react with ammonia to produce an organic product. Describe what is meant by the term halogenoalkane and explain why bromoethane is more reactive towards substitution reactions than fluoroethane.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
A halogenoalkane is an alkane in which one or more hydrogen atoms have been replaced by a halogen atom.
The reactivity of a halogenoalkane in substitution reactions depends on the strength of the carbon–halogen bond.
The C–F bond is stronger than the C–Br bond.
Because the C–F bond is stronger, it requires more energy to break, so fluoroethane reacts more slowly and is less reactive.
Bromoethane has a weaker C–Br bond, so it breaks more easily, making it more reactive in substitution reactions.
The reactivity of a halogenoalkane in substitution reactions depends on the strength of the carbon–halogen bond.
The C–F bond is stronger than the C–Br bond.
Because the C–F bond is stronger, it requires more energy to break, so fluoroethane reacts more slowly and is less reactive.
Bromoethane has a weaker C–Br bond, so it breaks more easily, making it more reactive in substitution reactions.
Examiner tips
- Use the exact definition of halogenoalkane; include the phrase ‘replaced by a halogen atom’.
- Show the bond‑strength comparison (C–F > C–Br) and link it to energy required to break the bond.
- Explain the consequence for substitution reactivity – weaker bond = easier to break = more reactive.
Common mistakes
- Confusing halogenoalkane with alkyl halide or mis‑identifying the bond strength order.
- Failing to explain that a weaker bond means less energy is needed to break it, thus higher reactivity.
- Using vague terms like ‘more reactive’ without linking to bond strength.
Mark scheme (5 marks)
- A halogenoalkane is an alkane in which one or more hydrogen atoms have been replaced by a halogen atom
- The reactivity depends on the strength of the carbon–halogen bond
- The C–F bond is stronger than the C–Br bond
- Because the C–F bond is stronger, it requires more energy to break, so fluoroethane reacts more slowly / is less reactive
- Bromoethane has a weaker C–Br bond so it breaks more easily, making it more reactive in substitution reactions
Key terms in this question
halogenoalkane · substitution reaction
Related
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- Decode the mark scheme abbreviations →
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