Key term
AQA GCSE Combined Science Chemistry 8464
Atomic Structure and the Periodic Table
Topic overviewAtoms, elements and compoundsWord equations, symbols and balanced equationsMixturesFrom the plum pudding model to the nuclear modelBohr, Chadwick and the modern model of the atomRelative electrical charges of subatomic particlesSize and mass of atomsRelative atomic mass and electronic structureThe periodic tableDevelopment of the periodic tableMetals and non-metalsGroup 0Group 1Group 7
Bonding, Structure, and the Properties of Matter
Topic overviewChemical bonds, including metallic bondingIonic bondingIonic compoundsCovalent bonding and how it is representedThe three states of matter and changes of statePredicting state, state symbols, and the limits of the particle modelProperties of ionic compoundsProperties of small moleculesPolymers and giant covalent structuresProperties of metals and alloys, and why metals conductDiamond and graphiteGraphene and fullerenes
Chemical Analysis
Chemical Changes
Topic overviewThe reactivity seriesMetal oxides, extraction, and redox in terms of electronsAcids reacting with metals, neutralisation and saltsSoluble saltsThe pH scale and neutralisationStrong and weak acidsThe process of electrolysis, and molten ionic compoundsUsing electrolysis to extract metalsElectrolysis of aqueous solutionsRepresentation of reactions at electrodes as half equations
Chemistry of the Atmosphere
Topic overviewThe Earth's early atmosphereHow oxygen increased and carbon dioxide decreasedThe gases in today's atmosphere, and which are greenhouse gasesHuman activities which contribute to an increase in greenhouse gases in the atmosphereGlobal climate change and carbon footprintsAtmospheric pollutants from fuels, and their effects
Energy Changes
Organic Chemistry
Quantitative Chemistry
The Rate and Extent of Chemical Change
Topic overviewMeasuring the mean rate of a reactionRate from graphs, and the gradient of a tangentFactors which affect the rates of chemical reactionsCollision theory and activation energyCatalystsReversible reactions and dynamic equilibriumThe effect of changing conditions on equilibriumThe effect of changing concentrationThe effect of temperature changes on equilibriumThe effect of pressure changes on equilibrium
Organic Chemistry
Why cracking is useful, and equations for it
- 3 things to know
- Chemistry Paper 2
Overview
Why small hydrocarbons are in demand and large fractions are cracked, the uses of alkenes, balancing cracking equations such as C₁₀H₂₂ to C₈H₁₈ and C₂H₄, and how modern life depends on hydrocarbons.
What you need to know
Answer each one before you reveal it.
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Key term
Explain why the numbers of carbon and hydrogen atoms must be the same on both sides of an equation for cracking.
Key term
Give one example that illustrates the usefulness of cracking.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Explain why there is such a high demand for hydrocarbons with small molecules.
Model answer
They make the best fuels, because they vaporise and ignite easily and flow readily.
- 2
Explain how cracking helps an oil refinery match its supply to demand.
Model answer
It converts fractions with large molecules, which are in low demand, into smaller molecules that are in high demand as fuels.
- 3
Which fractions from crude oil are the most likely to be cracked, and why?
Model answer
Fractions with large molecules and high boiling points, because there is comparatively little demand for them.
- 4
State one important use of the alkenes made by cracking.
Model answer
They are used to produce polymers.
- 5
Apart from making polymers, what are alkenes used for?
Model answer
They are used as starting materials for the production of many other chemicals.
- 6
Explain why alkenes are so valuable as starting materials for other chemicals.
Model answer
Their carbon–carbon double bond makes them reactive, so other atoms can be added across it to build new compounds.
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