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Using chemistry review
A summary of the whole Using Chemistry chapter, key words, and a mixed test covering bond energies and ΔH, fuels and combustion, electrochemical cells, rates of reaction, catalysts in industry, polymers and composites, and green chemistry.
Use this page to check the whole chapter. Read the summary, make sure you can explain every key word, then do the test without looking back.
Chapter summary
| Topic | What you need to know |
|---|---|
| 4A Energy and bonds | Breaking bonds takes energy in; making bonds gives energy out. ΔH = bonds broken − bonds made. Negative ΔH = exothermic, positive = endothermic. Energy profile: Eₐ from reactants to top of hump; ΔH from reactants to products. Catalysts lower Eₐ, not ΔH. Friction fire-making supplies Eₐ. Measure ΔH with Q = mcΔT (neutralisation ≈ −57 kJ/mol). Thermal decomposition (limestone → quicklime, yellow → red ochre) is endothermic. |
| 4B Fuels | Compare fuels by MJ/kg, MJ/L, g CO₂/MJ, pollutants, safety and cost. Complete combustion → CO₂ + H₂O (blue flame); incomplete → CO and soot (yellow flame). SO₂ from sulfur impurities and NOx from hot air in engines cause acid rain and smog. Combustion and respiration: same equation and total energy, but respiration is slow, enzyme-controlled and captures energy in ATP. |
| 4C Cells | Oxidation is loss, reduction is gain of electrons (OIL RIG). Metal extraction is reduction (blast furnace: CO; green steel: H₂). Galvanic cell: chemical → electrical; more reactive metal is the negative anode; electrons flow through the wire; salt bridge completes the circuit; voltage = difference in electrode potentials (Zn–Cu 1.10 V). Electrolytic cell: electrical → chemical (electroplating, aluminium smelting, charging). Oxidation always at the anode. Lithium-ion batteries; recycle batteries through B-cycle. |
| 4D Rates | Rate = change in amount ÷ time; measure gas volume, mass loss, colour or pH. Average rate vs initial rate (tangent). Rate graphs steepest at the start, level off when a reactant runs out. Collision theory: collide with at least Eₐ and the right orientation. Faster with higher concentration or pressure, higher temperature (about ×2 per 10 °C), greater surface area, catalysts and stirring. |
| 4E Catalysts | Catalysts give a lower-Eₐ pathway and aren't used up; surface catalysts need large surface areas. Catalytic converters (Pt, Pd, Rh) oxidise CO and hydrocarbons and reduce NOx. Haber process N₂ + 3H₂ ⇌ 2NH₃: compromise of ~450 °C, ~200 atm, iron catalyst, recycling. Enzymes in industry. Chlorine from CFCs catalysed ozone loss; Montreal Protocol 1987. |
| 4F Materials | Addition polymers (C=C monomers, no by-product) and condensation polymers (release water: nylon, PET). Linear, branched, lightly cross-linked (elastomer) and heavily cross-linked (thermoset) structures. Melt spinning and drawing make fibres. Composites: fibres in a matrix. Spinifex resin is a natural thermoplastic adhesive. Nanomaterials such as graphene. Judge new materials over their whole life. |
| 4G Green chemistry | Prevent waste; maximise atom economy = wanted product ÷ total reactants × 100%; use catalysts, safer solvents, renewable feedstocks and less energy. Resin codes identify polymers for recycling; Return and Earn; bag and single-use plastic bans. Safety data sheets; never mix cleaning products. Many careers use chemistry. |
Putting it together
The whole chapter is about controlling reactions to get what we want with the least harm. Bond energies tell us how much energy a reaction can release or must be given (4A), which decides whether it can be a fuel (4B) or a battery (4C). Collision theory tells us how fast it will go and how to change that (4D), and catalysts let industry make reactions fast without extreme conditions (4E). Knowing how atoms bond lets chemists design polymers, fibres and composites with exactly the properties they need (4F). Green chemistry asks the final question of every process: how can we get the product with the least waste, energy and hazard (4G)? The Haber process brings it all together: an exothermic, reversible reaction where engineers balance yield, rate, energy and cost to feed billions of people, and where green hydrogen may now cut its emissions.
Key words
activation energy · addition polymer · amide link · anode · atom economy · bond energy · catalyst · catalytic converter · cathode · collision theory · complete combustion · composite · condensation polymer · cross-link · drawing · elastomer · electrolysis · electrolytic cell · electroplating · endothermic · energy profile · enthalpy change (ΔH) · enzyme · equilibrium · exothermic · fibre · galvanic cell · green chemistry · Haber process · incomplete combustion · matrix · melt spinning · monomer · nanomaterial · oxidation · polymer · rate of reaction · redox · reduction · resin identification code · reversible reaction · salt bridge · spinneret · surface area · thermal decomposition · thermoplastic · thermoset · yield
Test yourself
A reaction absorbs 900 kJ breaking bonds and releases 750 kJ making bonds. It is
ΔH = 900 − 750 = +150 kJ: more energy in than out.
A gas heater burning with a yellow flame is most likely producing
A yellow flame shows incomplete combustion.
In a magnesium–copper galvanic cell, electrons flow
Magnesium is oxidised at the anode; electrons travel through the wire to the cathode.
Grinding a solid reactant into a powder increases the rate because
Greater surface area means more collisions per second.
Which statement about catalysts is correct?
A lower activation energy is how they speed up reactions.
A polymer that softens on heating and can be remoulded has
Thermoplastic chains can slide past each other when heated.
Making iron, 2Fe₂O₃ + 3C → 4Fe + 3CO₂, uses 355 g of reactants to make 223 g of iron. The atom economy is about
223 ÷ 355 × 100% = 63%.
Label the ammonia plant.
In the Haber process, what does each change do?
Order these fuels from most to least energy per kilogram.
Oxidation always happens at the . A reaction with a positive ΔH is . The energy needed to start a reaction is the energy. Fibres in a matrix make a . Reactions that join molecules with nothing left over have 100% atom .
A company plans to make a new biodegradable plastic from corn sugar. Using ideas from this chapter, discuss the chemistry (how the polymer could be made and how its structure affects its properties) and evaluate the social and environmental impacts of the plan.
Corn starch can be broken into glucose by enzymes, and bacteria can ferment the glucose into lactic acid. Lactic acid molecules have an –OH group at one end and a –COOH group at the other, so they can join by condensation polymerisation, releasing a water molecule at each link, to make polylactic acid (PLA). Its chains are linear and not cross-linked, so it is a thermoplastic: it softens when heated and can be moulded into cups and packaging. Using enzymes and catalysts at mild temperatures follows green chemistry principles, and the feedstock is renewable, so the plastic contains carbon recently taken from the air rather than from crude oil. However, growing corn uses land, water, fertiliser (made by the Haber process) and fuel, and using food crops for materials could raise food prices. PLA only breaks down in industrial composting at about 60 °C, so if it ends up in the ocean or in a home compost it lasts for years, and if put in the recycling bin it contaminates PET. The plan would be worthwhile if it used crop wastes rather than food, and if the company worked with councils on clear labelling and industrial composting collection; otherwise it risks being a "green" product that doesn't actually reduce harm.