📖 8 min read📅 Specification: AQA (8462), Edexcel (1CH0), OCR Gateway🧪 Paper 1 & Paper 2 Master Guide
Demystify chemistry formulas, reaction pathways, and mathematical calculations. From covalent bonding models and mole stoichiometry to electrolysis prediction rules, organic functional groups, and equilibrium equilibria — here are your high-yield revision notes.
Paper 1: Bonding, Quantitative Stoichiometry & Energy Changes
Topic 1 & 2: Atomic Structure & Bonding
Subatomic Particles: Protons (charge +1, mass 1), Neutrons (charge 0, mass 1), Electrons (charge -1, mass ~1/2000). Atomic number = protons; Mass number = protons + neutrons.
Ionic Bonding: Metal + Non-metal. Electrons transferred from metal to non-metal forming oppositely charged ions held by strong electrostatic forces in a giant ionic lattice. High melting points; conduct electricity only when molten or dissolved in water.
Covalent Bonding: Non-metal + Non-metal. Sharing electron pairs. Simple molecular substances (e.g. H₂O, CO₂, CH₄) have strong covalent bonds within molecules but weak intermolecular forces (low boiling points, non-conductors).
Giant Covalent Structures:
Diamond: Each carbon bonded to 4 carbons. Extremely hard, high melting point, electrical insulator.
Graphite: Each carbon bonded to 3 carbons in hexagonal layers with weak intermolecular forces between layers (slippery lubricant) and delocalised electrons (conducts electricity).
Metallic Bonding: Giant lattice of positive metal ions surrounded by a sea of delocalised electrons. High thermal & electrical conductivity; malleable because layers can slide.
Topic 3: Quantitative Chemistry (The Math)
Moles Formula:Moles = Mass (g) / Mr.
Concentration:Concentration (g/dm³ or mol/dm³) = Mass or Moles / Volume (dm³). Note: 1 dm³ = 1,000 cm³.
Percentage Yield:(Actual Mass Produced / Theoretical Maximum Mass) × 100.
Atom Economy:(Mr of Desired Product / Total Mr of All Reactants) × 100. Higher atom economy produces less industrial waste.
Limiting Reactant: The reactant that is completely consumed first, dictating the maximum quantity of product formed.
Topic 4: Chemical Changes & Electrolysis
Reactivity Series: K > Na > Ca > Mg > Al > [Carbon] > Zn > Fe > [Hydrogen] > Cu > Ag > Au. Metals below carbon extracted via reduction with carbon; metals above carbon require electrolysis.
Acid Reactions:
Acid + Metal → Salt + Hydrogen (MASH)
Acid + Base/Alkali → Salt + Water
Acid + Carbonate → Salt + Water + Carbon Dioxide
Electrolysis (PANIC: Positive Anode, Negative Is Cathode):
Oxidation: Loss of electrons (at positive Anode).
Reduction: Gain of electrons (at negative Cathode).
OIL RIG: Oxidation Is Loss, Reduction Is Gain of electrons.
Topic 5: Energy Changes
Exothermic Reactions: Energy released to surroundings (temperature rises; ΔH is negative). E.g. Combustion, neutralisation.
Endothermic Reactions: Energy absorbed from surroundings (temperature falls; ΔH is positive). E.g. Thermal decomposition, citric acid + sodium hydrogencarbonate.
Bond Energy Calculation:
Energy Change (ΔH) = Total Energy to BREAK bonds (reactants) - Total Energy RELEASED forming bonds (products).
Remember: BEnDO MEXo — Breaking is Endothermic, Making is Exothermic.
Paper 2: Reaction Rates, Organic Chemistry & Atmosphere
Topic 6 & 7: Rates of Reaction & Organic
Factors Increasing Rate: Increasing concentration/pressure (more particles per unit volume → more frequent collisions), increasing surface area to volume ratio, increasing temperature (particles have more kinetic energy and greater proportion exceed activation energy Ea), adding a catalyst (provides alternative reaction pathway with lower Ea).
Crude Oil & Fractional Distillation: Mixture of hydrocarbons separated based on boiling points. Shorter alkanes boil off at cooler top column (volatile, flammable, low viscosity).
Cracking: Thermal decomposition of long-chain alkanes into high-demand short-chain alkanes (fuels) and alkenes (plastics). Catalytic cracking uses hot zeolite; steam cracking uses high temperatures and steam.
Evolution of Atmosphere: Early atmosphere mainly CO₂ from volcanic eruptions. Algae and green plants evolved ~2.7 billion years ago, producing O₂ via photosynthesis and locking away carbon in fossil fuels and sedimentary rocks.
Potable Water: Water safe to drink (low levels of dissolved salts and microbes). Fresh water treated via filtration (sand beds) and sterilisation (chlorine, ozone, or UV). Sea water desalinated via distillation or reverse osmosis (high energy cost).
💡 Key Takeaway
Golden Electrolysis Tip: In molten lead bromide (PbBr₂), Lead forms at the cathode (Pb²⁺ + 2e⁻ → Pb, silver bead) and Bromine gas forms at the anode (2Br⁻ → Br₂ + 2e⁻, red-brown pungent vapour). Never confuse molten with aqueous solutions!
Active Recall: GCSE Chemistry Formulas & Tests
📇 Flashcards: GCSE Chemistry Mastery Deck
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Why do giant ionic lattices conduct electricity when molten but NOT when solid?
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In solid state, ions are locked in fixed lattice positions by strong electrostatic bonds. When molten or dissolved, ions become free to move and carry electrical charge.
💡 Spaced Repetition: Cards marked "Review Again" will repeat at the end of the session.
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Frequently Asked Questions
There are three primary mole formulas: 1) For solids: Moles = Mass (g) / Relative Formula Mass (Mr). 2) For solutions: Moles = Concentration (mol/dm³) × Volume (dm³). 3) For gases at room temperature and pressure: Moles = Volume (dm³) / 24.
At the Cathode (negative electrode): Hydrogen is produced unless the metal is less reactive than hydrogen (Copper, Silver, Gold). At the Anode (positive electrode): Halide ions (Cl⁻, Br⁻, I⁻) form halogen gases. If no halide is present, hydroxide (OH⁻) is discharged to produce Oxygen gas (4OH⁻ → O₂ + 2H₂O + 4e⁻).
If a system at equilibrium is disturbed, the equilibrium shifts to counteract the change: 1) Increasing temperature shifts in the endothermic direction. 2) Increasing pressure shifts to the side with fewer gas molecules. 3) Increasing reactant concentration shifts towards products.
Alkanes are saturated hydrocarbons with single C-C bonds only (general formula CnH2n+2). Alkenes are unsaturated hydrocarbons containing a functional C=C double bond (general formula CnH2n), which decolourises bromine water from orange-brown to colourless.
