Overview
This lecture covers key points from AQA Chemistry Paper 2 topics 6–10, including rates of reaction, organic chemistry, chemical analysis, atmospheric chemistry, and using resources, suitable for both combined Trilogy and separate Chemistry students.
Rates of Reaction & Equilibrium
- Rate of reaction = change in quantity (mass/volume) ÷ time.
- Mean rate is measured over an interval; draw a tangent to find rate at a specific time.
- Increase rate by: higher concentration, pressure, surface area, temperature, or adding a catalyst (not used up in reaction).
- Reversible reactions can proceed both directions; at equilibrium, rates of forward and reverse reactions are equal.
- Le Chatelier’s Principle: changing conditions (pressure, concentration, temperature) shifts equilibrium to counteract the change.
Organic Chemistry & Crude Oil
- Organic compounds contain carbon backbones; crude oil is mostly hydrocarbons.
- Alkanes (single bonds): general formula CnH2n+2, names end in "-ane."
- Fractional distillation separates crude oil into fractions by boiling point.
- Longer alkanes have higher boiling points, are more viscous, and less flammable.
- Alkenes (contain C=C double bond): unsaturated, test with bromine water (turns colorless).
- Cracking breaks long alkanes into shorter alkanes and alkenes, using high temperature and catalyst.
Polymers & Other Organic (Triple Only)
- Alkenes can form polymers (addition polymerization, e.g. polyethene).
- Alcohols have -OH group, react with sodium and oxygen, can be oxidized to carboxylic acids.
- Condensation polymerization joins monomers with two functional groups, producing water as a by-product (e.g., polyesters).
- Amino acids (NH2 and COOH groups) polymerize to form proteins; DNA is a double-helix polymer of nucleotides.
Chemical Analysis
- Pure substances have specific melting/boiling points; formulations are mixtures with set ratios.
- Chromatography separates mixtures; calculate Rf value = (distance substance moves) ÷ (distance solvent moves).
- Test gases: hydrogen (squeaky pop), oxygen (relights glowing splint), CO2 (limewater cloudy), chlorine (bleaches damp litmus).
- Flame tests for metal ions: lithium (crimson), sodium (yellow), potassium (lilac), calcium (orange-red), copper (green).
- Precipitation and chemical tests for ions (e.g., carbonates, halides, sulfates) and instrumental analysis like flame emission spectroscopy.
Atmospheric Chemistry
- Early atmosphere: mostly nitrogen, carbon dioxide from volcanoes; CO2 dissolved in oceans, locked in rocks/fossil fuels.
- Photosynthesis reduced CO2, increased O2.
- Greenhouse gases (CO2, water vapor, methane) trap heat; increased CO2 raises global temperatures.
- Pollutants: carbon monoxide (toxic), sulfur dioxide (acid rain), nitrogen oxides (respiratory problems), particulates (health issues).
Using Resources & Sustainability
- Potable water: low salt/microbe levels, made by filtering, sterilizing, sometimes desalinating (energy intensive).
- Waste water treated by screening, sedimentation, and aerobic/anaerobic digestion.
- Metals extracted by mining, electrolysis, displacement, phytomining, or bioleaching.
- Life Cycle Assessment (LCA) evaluates environmental impact from production to disposal.
- Recycling saves resources and energy; metals and glass can be recycled repeatedly.
- Corrosion: iron rusts; prevention includes coatings, galvanizing (zinc sacrificial layer).
- Alloys (mixtures of metals) are stronger; steel, bronze, brass, and gold jewelry are examples.
- Glass, ceramics, composites, and polymers (thermosoftening or thermosetting) have varied uses based on properties.
Haber Process & Fertilizers
- Haber process produces ammonia from nitrogen and hydrogen using a catalyst at 450°C, 200 atm pressure.
- Ammonia used for fertilizers (NPK: nitrogen, phosphorus, potassium) to support plant growth.
Key Terms & Definitions
- Rate of Reaction — change in reactant/product quantity per unit time.
- Equilibrium — state where forward and reverse reaction rates are equal.
- Alkane — hydrocarbon with single C–C bonds, saturated.
- Alkene — hydrocarbon with at least one C=C double bond, unsaturated.
- Polymerization — joining small molecules (monomers) to form long chains (polymers).
- Chromatography — technique to separate mixtures and identify components.
- Life Cycle Assessment (LCA) — evaluating environmental impact of a product over its lifetime.
- Potable Water — water safe to drink, low in dissolved salts and microbes.
Action Items / Next Steps
- Review key experiments (rates, chromatography, water treatment).
- Memorize flame test colors and ion test results.
- Practice drawing and interpreting energy and polymerization diagrams.
- Complete past paper questions on equilibria and organic reactions.