GCSE Chemistry Paper 2 Overview

Topics Covered

• Rates of Reactions
• Organic Chemistry
• Chemical Analysis
• Atmospheric Chemistry
• Using Resources

Rates of Reactions

• Definition: Measurement of how quickly a reaction happens (amount of something per unit time).
• Common Measurement: Volume of gas produced.
• **Factors Affecting Rate:"
  • Surface Area: More surface area increases reaction rate.
  • Concentration/Pressure: Higher concentration/pressure increases collision frequency.
  • Temperature: Higher temperature increases both collision frequency and energy.
  • Catalysts: Lower activation energy to increase reaction rate.
• Experiments:
  • Gas Syringe: Collect gas to measure volume.
  • Sodium Thiosulfate and Hydrochloric Acid: Measure time for solution to turn cloudy.**

Equilibrium and Le Chatelier's Principle

• Reversible Reactions: These reactions can proceed in both forward and backward directions.
• Dynamic Equilibrium: In a closed system, forward and backward reaction rates are equal.
• Le Chatelier's Principle: If equilibrium is disturbed, the system will adjust to counteract the change.
  • Adding more reactants shifts equilibrium to the right (forward reaction).
  • Increasing pressure favors side with fewer molecules.

Haber Process

• Used to make ammonia (NH3).
• Reaction: N2 + 3H2 → 2NH3
• Conditions: High pressure (200 atm), compromise temperature (450°C), iron catalyst.
• Increasing pressure & lowering temperature increases yield but is expensive/slow.

Organic Chemistry

• Hydrocarbons: Compounds containing only hydrogen and carbon.
• Crude Oil: Mixture of hydrocarbons, mostly alkanes.
• Fractional Distillation: Separates crude oil into fractions based on boiling points.
  • Fractions from top (lowest boiling point) to bottom (highest): LPG, Petrol, Paraffin, Diesel, Fuel Oil, Bitumen.

Alkanes and Alkenes

• Alkanes: Saturated hydrocarbons (single bonds). Methane (CH4), Ethane (C2H6), Propane (C3H8), etc.
• Alkenes: Unsaturated hydrocarbons (at least one double bond). Ethene (C2H4), Propene (C3H6).
  • Combustion: Alkanes burn to produce CO2 and H2O. Incomplete combustion produces CO (dangerous).
  • Bromine Water Test: Differentiates alkenes (decolorizes bromine water) from alkanes.
  • Cracking: Converts long-chain alkanes to shorter alkanes and alkenes.

Reactions of Hydrocarbons

• Alkenes react with hydrogen to form alkanes.
• React with halogens (e.g., bromine) to form bromoalkanes.
• React with water to form alcohols (e.g., ethanol).

Other Organic Compounds

• Alcohols: Contain OH group. Example: Ethanol.
• Carboxylic Acids: Contain COOH group.
• Esters: Formed from carboxylic acids and alcohols, often have pleasant smells.

Polymers

• Addition Polymerization: Joins monomers with double bonds (e.g., ethene → polyethene).
• Condensation Polymerization: Joins monomers with different functional groups, releasing small molecules (e.g., water).
• Biological Polymers: Proteins (amino acids), DNA (nucleotides), carbohydrates (glucose).