Edexcel GCSE Chemistry: Organic Chemistry - Hydrocarbons

Edexcel GCSE Chemistry: Organic Chemistry - Hydrocarbons

This tutorial covers the properties, uses, and reactions of alkanes and alkenes, which are key topics for Edexcel GCSE Chemistry Paper 2.

Introduction to Hydrocarbons

Hydrocarbons are organic compounds made up of only carbon (C) and hydrogen (H) atoms. They form the basis of many important materials, including fuels and plastics.

Hydrocarbons are classified into two main types:

• Alkanes: These are saturated hydrocarbons, meaning they only contain single bonds between carbon atoms.
• Alkenes: These are unsaturated hydrocarbons, meaning they contain at least one double bond between carbon atoms.

Alkanes

Properties of Alkanes

• General formula: CnH2n+2, where n is the number of carbon atoms.
• Saturated: Only contain single bonds.
• Non-polar: The electronegativity difference between carbon and hydrogen is small, making them non-polar molecules.
• Low reactivity: Due to their strong C-H and C-C single bonds.
• Flammable: They readily burn in air, releasing energy.
• Boiling point increases with chain length: Longer chains have stronger intermolecular forces, leading to higher boiling points.

Uses of Alkanes

• Fuels: Methane (CH4), propane (C3H8), and butane (C4H10) are major components of natural gas and liquefied petroleum gas (LPG).
• Petrochemicals: Alkanes are the starting materials for many important chemicals, including plastics, detergents, and medicines.

Reactions of Alkanes

• Combustion: Alkanes react with oxygen to produce carbon dioxide, water, and energy.
• Substitution reactions: Alkanes can react with halogens (e.g., chlorine, bromine) in the presence of ultraviolet light to form haloalkanes.

Alkenes

Properties of Alkenes

• General formula: CnH2n, where n is the number of carbon atoms.
• Unsaturated: Contains at least one double bond between carbon atoms.
• More reactive than alkanes: The double bond is weaker and more susceptible to attack.
• Can undergo addition reactions: The double bond can break open to form single bonds.

Uses of Alkenes

• Polymers: Ethene (C2H4) is used to produce polyethylene, a widely used plastic.
• Chemicals: Propene (C3H6) is used to make polypropylene and other chemicals.
• Fuels: Alkenes are found in petroleum and are used as fuel components.

Reactions of Alkenes

• Addition reactions: Alkenes readily undergo addition reactions, where the double bond breaks and atoms are added to the carbon atoms. Examples include:
  • Halogenation: Addition of halogens (e.g., bromine) to form dihaloalkanes.
  • Hydrogenation: Addition of hydrogen to form alkanes.
  • Hydration: Addition of water to form alcohols.
• Combustion: Alkenes also burn in air, producing carbon dioxide and water.

Summary

This tutorial provided a basic introduction to alkanes and alkenes, covering their properties, uses, and reactions. Remember to revise these concepts thoroughly and practice answering exam questions. Understanding hydrocarbons is crucial for your success in Edexcel GCSE Chemistry.