Overview
This lecture provides a comprehensive summary of GCSE Chemistry Paper 2, covering key topics such as rates of reaction, equilibrium, organic chemistry, chemical analysis, the atmosphere, and the use of Earth's resources.
Rates of Reaction
- Rate of reaction = amount of reactants used or products made per time.
- Reactant vs. time graph curves downward; product vs. time graph curves upward.
- Steeper graph gradient means a faster reaction rate; the rate is fastest at the start and slows over time.
- For curved graphs, draw a tangent to measure the gradient (rate) at a specific point.
- Factors increasing reaction rate: higher temperature, higher concentration/pressure, greater surface area, and use of a catalyst.
- Activation energy: minimum energy needed for a reaction to occur.
- Catalyst: substance that speeds up a reaction by providing an alternative pathway with lower activation energy.
Equilibrium
- Reversible reaction: products can react to reform reactants; direction can be changed by altering conditions.
- In a closed system, equilibrium is reached when forward and backward reaction rates are equal and concentrations are constant.
- Le Chatelier’s Principle: system shifts to counteract changes in temperature, pressure, or concentration.
- Increase temperature shifts equilibrium to endothermic side; increase pressure shifts to side with fewer moles.
Organic Chemistry
- Crude oil: non-renewable, made from ancient biomass, mostly hydrocarbons.
- Fractional distillation separates hydrocarbons based on boiling points.
- Longer hydrocarbons have higher boiling points, are thicker (more viscous), and less flammable.
- Alkanes: saturated hydrocarbons (single bonds); general formula CnH2n+2.
- Alkanes combust to form CO₂ and water.
- Cracking breaks long hydrocarbons into smaller alkanes and alkenes.
- Alkenes: unsaturated hydrocarbons (contain double bonds), more reactive than alkanes, turn bromine water colorless.
Chemical Analysis
- Pure substances have set melting/boiling points; impurities change these values.
- Formulations: mixtures designed for specific purposes (e.g., paint, medicine, alloys).
- Chromatography separates mixture components based on solubility; RF value = distance by substance ÷ distance by solvent.
- Gas tests: hydrogen (squeaky pop), oxygen (relights glowing splint), CO₂ (cloudy limewater), chlorine (bleaches blue litmus paper).
The Atmosphere
- Early atmosphere formed from volcanic gases; mainly water vapor, CO₂, nitrogen.
- Oxygen increased due to photosynthesis by algae/plants, enabling animal evolution.
- Modern atmosphere: 78% nitrogen, 21% oxygen, ~1% other gases; CO₂ is about 0.04%.
- Greenhouse gases (CO₂, methane, water vapor) trap heat; human activities (fossil fuels, farming, deforestation) increase greenhouse gases leading to global warming.
- Other pollutants: carbon monoxide (toxic), particulates (respiratory issues), sulfur dioxide/nitrogen oxides (acid rain).
Using Resources
- Renewable and non-renewable resources; conservation important (recycling, reusing).
- Metals are extracted from ores; low-grade ores use phytomining (plants absorb metals) or bioleaching (bacteria).
- Potable water made by filtering and sterilizing fresh water or desalination (distillation/reverse osmosis).
- Wastewater is treated by screening, sedimentation, aerobic and anaerobic bacteria treatment.
- Life cycle assessment evaluates product impact across extraction, manufacture, use, and disposal.
Key Terms & Definitions
- Rate of Reaction — speed at which reactants are converted to products.
- Activation Energy — minimum energy needed for a reaction.
- Catalyst — increases reaction rate without being used up.
- Reversible Reaction — reaction where products can become reactants.
- Equilibrium — state where forward and backward reaction rates are equal.
- Le Chatelier’s Principle — predicts equilibrium shifts with condition changes.
- Hydrocarbon — compound of hydrogen and carbon only.
- Saturated Hydrocarbon — only single bonds (alkanes).
- Unsaturated Hydrocarbon — contains double bonds (alkenes).
- Formulation — mixture designed for a specific use.
- RF Value — ratio for chromatography to identify substances.
- Greenhouse Gas — gases that trap heat in the atmosphere.
- Phytomining — extracting metals using plants.
- Bioleaching — extracting metals using bacteria.
- Potable Water — water safe for drinking.
Action Items / Next Steps
- Review graphs and calculation methods for reaction rates.
- Memorize tests for identifying gases.
- Practice life cycle assessment steps for products.
- Complete any assigned exercises or past paper questions on these topics.