Properties of Hydrocarbons and their Dependence on Molecular Size

Overview

• Hydrocarbons are an important topic often featured in exams.
• Understanding their properties in relation to molecule size is crucial.

Types of Hydrocarbons

• Alkanes: A family of hydrocarbons.
  • First four alkanes: Methane, Ethane, Propane, Butane.
  • Be prepared to draw these alkanes in exams.

Key Properties of Hydrocarbons

1. Viscosity

• Definition: Thickness of a fluid; high viscosity means the fluid flows slowly.
  • Example: Honey is a fluid with high viscosity.
• Relation to Hydrocarbon Size:
  • Larger hydrocarbon molecules = higher viscosity.
  • Long chain hydrocarbons flow very slowly (extremely viscous).

2. Flammability

• Definition: Ease of combustion (burning) of a hydrocarbon.
• Relation to Hydrocarbon Size:
  • Short chain hydrocarbons are highly flammable (e.g., Methane).
  • As molecular size increases, flammability decreases.
  • Long chain hydrocarbons are difficult to burn.

3. Boiling Point

• Definition: Temperature at which a liquid turns into a gas.
• Relation to Hydrocarbon Size:
  • Short chain hydrocarbons have low boiling points.
  • These hydrocarbons are often gases at room temperature due to low boiling points.
  • As molecular size increases, boiling point increases.
  • Long chain hydrocarbons have high boiling points.

Additional Resources

• Practice questions available in the revision workbook, accessible via the provided link.
• Next video will cover how hydrocarbons combust.