CuO + H₂ → Cu + H₂O
CuO loses O → reduced · H₂ gains O → oxidised
Zn + Cu²⁺ → Zn²⁺ + Cu
Zn loses e⁻ (oxidised), Cu²⁺ gains e⁻ (reduced)

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

oxidising agent: causes oxidation, is itself reduced
reducing agent: causes reduction, is itself oxidised

cathode: Na⁺ + e⁻ → Na
anode: 2Cl⁻ → Cl₂ + 2e⁻
molten binary compound → metal at cathode, non-metal at anode
works only when molten/aq — ions must be free to move

CuSO₄(aq) with Cu electrodes: anode Cu → Cu²⁺ + 2e⁻ (dissolves), cathode Cu²⁺ + 2e⁻ → Cu
purify: impure Cu = anode, pure Cu = cathode
electroplating: object = cathode, plating metal = anode

2 different metals in an electrolyte → electricity
more reactive metal = negative terminal (loses e⁻)
bigger reactivity gap → bigger voltage
H₂ fuel cell: 2H₂ + O₂ → 2H₂O → electricity, only water made

a more reactive metal pushes a less reactive one out of its compound
Zn + CuSO₄ → ZnSO₄ + Cu
blue fades, pink-brown solid forms
also from oxides: Mg + CuO → MgO + Cu

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

carbon reduces oxides of Zn, Fe, Pb, Cu
hydrogen reduces oxides of Fe, Pb, Cu

K, Na carbonates: no change
others → oxide + CO₂, easier the less reactive the metal
CuCO₃ (green) → CuO (black) + CO₂

needs oxygen AND water · rust = hydrated iron(III) oxide
salt water and acid speed it up

barrier: paint, grease/oil, plastic coating
galvanising: coat with zinc
sacrificial protection: attach Mg/Zn blocks — they corrode instead of iron

breaking bonds takes in energy (endo)
making bonds gives out energy (exo)
ΔH = energy to break − energy released making

H₂ + Cl₂ → 2HCl · bonds: H–H 436, Cl–Cl 242, H–Cl 431 kJ/mol
ΔH = (436 + 242) − 2(431) = −184 kJ/mol → exothermic

steeper = faster
flat = reaction stopped (one reactant used up)
half the reactant → final volume halves
rate = gradient

measure: gas syringe, mass loss on a balance, time for a cross to disappear

speed up a reaction, chemically unchanged at the end
industrial: Fe (Haber), Ni (making margarine)
enzymes = biological catalysts (proteins, best at an optimum temperature)

change one variable, keep others constant (same mass, volume, temperature)
measure gas volume at fixed time intervals

N₂ from fractional distillation of liquid air
H₂ from cracking crude oil (hydrocarbons)

450 °C · 200 atm · iron catalyst
unreacted gases are recycled
NH₃ removed by cooling (liquefies)

lower temperature → more ammonia but too slow
higher pressure → more ammonia but costly & dangerous
catalyst → faster, same yield

big alkane → smaller alkane + alkene (+ H₂)
high temp + catalyst
C₁₀H₂₂ → C₈H₁₈ + C₂H₄
why: more demand for smaller fuel molecules

same general formula · same functional group · similar chemical properties · physical properties change gradually (b.p. ↑ as chain grows)
isomers: same molecular formula, different structure (butane / methylpropane)

polyunsaturated: many C=C bonds
margarine: add H₂ to vegetable oil (Ni catalyst) → solid

bioethanol from sugarcane is renewable; CO₂ released on burning was taken in by the plants while growing

fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
yeast, warm, no oxygen
ethene + steam (catalyst, high temp & pressure) → ethanol

oxygen in air (wine turns to vinegar) or acidified KMnO₄ (purple → colourless)
combustion: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

acid + alcohol ⇌ ester + water
conc. H₂SO₄ catalyst, heat · sweet, fruity smell
ethanoic acid + ethanol → ethyl ethanoate

alcohol part first (-yl) + acid part (-oate)
methanol + propanoic acid → methyl propanoate
CH₃COOC₂H₅ = ethyl ethanoate

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

monomers join and lose a small molecule (water)
nylon = polyamide (–CONH– amide link)
Terylene = polyester (–COO– ester link)

clothing, curtains, fishing line, parachutes, sleeping bags

most plastics are non-biodegradable → fill landfills, harm marine life
burning releases toxic gases

physical: melt and remould into pellets
chemical: crack / depolymerise into fuel or new monomers
issues: sorting cost, quality drops, need public effort

CO₂ and CH₄ trap heat → global warming → extreme weather, melting polar ice

photosynthesis removes CO₂; respiration & combustion add CO₂ → balance keeps CO₂ steady

catalytic converter (redox): 2CO + 2NO → 2CO₂ + N₂
calcium carbonate: neutralises acidic lakes & removes SO₂ from power station flue gas (desulfurisation)

absorbs harmful UV radiation
destroyed by chlorine from CFCs (old aerosols, fridges)