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THE CHAPTERS
🔁
CH 1
Redox
OIL RIG.
🏆
CH 2
Reactivity, Metals & Rusting
K Na Ca Mg Zn Fe Pb H Cu Ag.
🌡️
CH 3
Chemical Energetics
Exo releases, endo absorbs.
⏱️
CH 4
Rate of Reactions
More effective collisions.
🛢️
CH 5
Fuels & Hydrocarbons
Alkanes single, alkenes C=C.
🍶
CH 6
Alcohols & Acids
–OH and –COOH.
🧵
CH 7
Polymers
Many monomers joined.
🌍
CH 8
Air Quality
78% N₂, 21% O₂.
📌 NOTESome schools start a few of these (e.g. energetics, rates, redox) in Sec 3.
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Sec 4 Combined Science (Chem) · SEC K326
🔁
1
Redox
oxidation, reduction, oxidation states, agents
BIG IDEAOIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain. Both always happen together.
Oxidation
Reduction
Oxygen
gains O
loses O
Hydrogen
loses H
gains H
Electrons
loses e⁻
gains e⁻
Oxidation state
increases ↑
decreases ↓
Example
CuO + H₂ → Cu + H₂O CuO loses O → reduced · H₂ gains O → oxidised Zn + Cu²⁺ → Zn²⁺ + Cu Zn loses e⁻ (oxidised), Cu²⁺ gains e⁻ (reduced)
Oxidation state rules
element on its own = 0 simple ion = its charge (Fe³⁺ = +3) O = −2, H = +1 compound total = 0 · ion total = charge S in SO₄²⁻: x + 4(−2) = −2 → +6
Test
Add to unknown
Positive result
Means unknown is
KI(aq)
colourless KI
turns brown (I₂ formed)
an oxidising agent
acidified KMnO₄(aq)
purple
turns colourless
a reducing agent
Agents
oxidising agent: causes oxidation, is itself reduced reducing agent: causes reduction, is itself oxidised
⚠ TRAPThe oxidising agent is the one that gets reduced — easy to mix up. Use oxidation states to check.
Sec 4 Combined Science (Chem) · SEC K326
🏆
2
Reactivity Series, Metals & Rusting
reactions, displacement, extraction, rusting
BIG IDEAMore reactive = loses electrons more easily = forms positive ions more readily. Please Send Cats, Monkeys, Zebras, In Lovely Hot Cages, Ah.
Metal
Cold water
Steam
Dilute HCl
Extracted by
K
✓ violent
—
dangerous
electrolysis
Na
✓ vigorous
—
dangerous
electrolysis
Ca
✓ steady
—
✓ vigorous
electrolysis
Mg
very slow
✓ burns
✓
electrolysis
Zn
✗
✓
✓
carbon
Fe
✗
✓ (red hot)
✓ slow
carbon
Pb
✗
✗
very slow
carbon
(H)
Cu
✗
✗
✗
found / heat
Ag
✗
✗
✗
found native
Displacement
a more reactive metal pushes a less reactive one out of its compound Zn + CuSO₄ → ZnSO₄ + Cu blue fades, pink-brown solid forms
🧲 Extraction
metals above carbon → electrolysis of molten compound metals below carbon → heat oxide with carbon least reactive → found as the metal more reactive = harder to extract
🟤 Rusting
needs oxygen AND water · rust = hydrated iron(III) oxide salt water and acid speed it up
Stop rusting
barrier: paint, grease/oil, plastic coating
Sec 4 Combined Science (Chem) · SEC K326
🌡️
3
Chemical Energetics
exothermic & endothermic
BIG IDEAExothermic gives out heat → temperature rises. Endothermic takes in heat → temperature falls.
✍ WRITE THIS"The reaction is exothermic because the temperature of the mixture increased, showing heat was released to the surroundings."
⚠ TRAPIn an endothermic reaction the beaker feels cold — heat is taken from the surroundings (your hand).
Sec 4 Combined Science (Chem) · SEC K326
⏱️
4
Rate of Reactions
collision theory, graphs
BIG IDEAFaster reaction = more effective collisions per second (particles hit with enough energy).
Increase…
Effect
Why
🧪 concentration
faster
more particles per unit volume → more frequent collisions
🎈 pressure (gases)
faster
particles closer together → more frequent collisions
🔨 surface area (smaller pieces)
faster
more particles exposed → more frequent collisions
🔥 temperature
faster
particles have more energy → more collide with enough energy, and more often
same final volume if same amount of limiting reactant
Reading the graph
steeper = faster flat = reaction stopped (one reactant used up) half the reactant → final volume halves rate = gradient
⚠ TRAP"More collisions" is not enough — write "more frequent effective collisions".
Sec 4 Combined Science (Chem) · SEC K326
🛢️
5
Fuels & Hydrocarbons
crude oil, alkanes, alkenes, cracking
BIG IDEACrude oil is a mixture of hydrocarbons separated by fractional distillation. Alkanes have single bonds; alkenes have a C=C.
down the column: bigger molecules, higher b.p., more viscous
Fraction
Use
refinery gas
cooking / heating fuel
petrol
car fuel
naphtha
chemical feedstock
kerosene
aircraft fuel
diesel
buses, lorries
fuel oil
ships, power stations
bitumen
roads
Alkanes
Alkenes
Formula
CₙH₂ₙ₊₂
CₙH₂ₙ
Bonds
single — saturated
C=C — unsaturated
Members
methane CH₄ · ethane C₂H₆ · propane C₃H₈
ethene C₂H₄ · propene C₃H₆
Bromine water
stays orange/brown
orange → colourless
Reactions
combustion; substitution with Cl₂ (UV light)
combustion; addition: + Br₂, + H₂; polymerisation
Cracking
big alkane → smaller alkane + alkene (+ H₂) high temp + catalyst C₁₀H₂₂ → C₈H₁₈ + C₂H₄ why: more demand for smaller fuel molecules
Homologous series
same general formula · same functional group · similar chemical properties · physical properties change gradually (b.p. ↑ as chain grows)
Food
polyunsaturated: many C=C bonds margarine: add H₂ to vegetable oil (Ni catalyst) → solid
🌱 Biofuel
bioethanol from sugarcane is renewable; CO₂ released on burning was taken in by the plants while growing
Sec 4 Combined Science (Chem) · SEC K326
🍶
6
Alcohols & Carboxylic Acids
functional groups, fermentation, oxidation
BIG IDEAAlcohols have –OH; carboxylic acids have –COOH. Oxidising an alcohol makes the acid.
Alcohols
Carboxylic acids
Functional group
–OH
–COOH (–CO₂H)
Members
methanol, ethanol, propanol
ethanoic acid (vinegar)
Reactions
combustion; oxidation → acid
weak acid
Making ethanol
fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ yeast, warm, no oxygen
Ethanol → ethanoic acid
oxygen in air (wine turns to vinegar) or acidified KMnO₄ (purple → colourless) combustion: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
ethanol C₂H₅OH · ethanoic acid CH₃COOH — draw every bond
⚠ TRAPDraw full structural formulae with every bond shown. Carbon always has 4 bonds, oxygen 2, hydrogen 1.
Sec 4 Combined Science (Chem) · SEC K326
🧵
7
Polymers
addition polymers, plastics, recycling
BIG IDEAA polymer is a huge molecule made of many small monomers joined together.
ethene → poly(ethene): C=C opens up
Addition polymerisation
monomer has a C=C double bond breaks, monomers join in a chain uses of poly(ethene): plastic bags, clingfilm monomer ⇄ polymer: draw 2 C atoms of the repeat unit
🗑️ Problems
most plastics are non-biodegradable → fill landfills, harm marine life burning releases toxic gases
♻️ Recycling
physical: melt and remould into pellets chemical: crack into fuel or new monomers issues: sorting cost, quality drops, need public effort