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7.3 Properties and combustion of hydrocarbons

5 exam questions worth 9 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.

0 / 9

1
Multiple choice [1 mark]

How does the viscosity of hydrocarbons change as the chain length increases?

Choose one answer.

Correct Not quite: the answer is It increases

Mark scheme

A

Model answer

A: longer chains are thicker and flow less easily.

2
Short answer [2 marks]

Explain why short-chain hydrocarbons are better fuels than long-chain hydrocarbons.

Mark scheme

  • more flammable / ignite more easily (1)
  • lower boiling point / evaporate easily / less viscous so flow easily (1)

Model answer

Short-chain hydrocarbons catch fire more easily and evaporate easily, and they flow well.

Your mark
3
Short answer [2 marks]

Name the products of the complete combustion of a hydrocarbon.

Mark scheme

  • carbon dioxide (1)
  • water (1)

Model answer

Carbon dioxide and water.

Your mark
4
Short answer [2 marks]

Write a balanced equation for the complete combustion of propane, C3H8.

Mark scheme

  • correct products CO2 and H2O (1)
  • C3H8 + 5O2 → 3CO2 + 4H2O (1)

Model answer

C3H8 + 5O2 → 3CO2 + 4H2O

Your mark
5
Short answer [2 marks]

Explain why boiling point increases with chain length.

Mark scheme

  • longer molecules have stronger intermolecular forces (1)
  • more energy needed to overcome them (1)

Model answer

Longer molecules have stronger forces between them, so more energy is needed to separate them.

Your mark
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