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
Cracking, and testing alkenes with bromine water
- 3 things to know
- Chemistry Paper 2
Overview
Cracking as the thermal decomposition of large hydrocarbons into smaller molecules, catalytic cracking and steam cracking and their conditions, the alkanes and unsaturated alkenes produced, and the bromine water test, which turns from orange to colourless with an alkene.
What you need to know
Answer each one before you reveal it.
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Key term
What is cracking?
Key term
Explain why cracking one large hydrocarbon molecule always gives more than one product molecule.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is cracking?
Model answer
Cracking is the breaking down of large hydrocarbon molecules into smaller, more useful molecules.
- 2
What type of reaction is cracking, in terms of what heat does to the molecules?
Model answer
It is a thermal decomposition reaction, because heat breaks one large molecule down into smaller ones.
- 3
Explain why cracking one large hydrocarbon molecule always gives more than one product molecule.
Model answer
The large molecule is split into two or more smaller molecules, and every atom must be conserved.
- 4
Name two methods of cracking.
Model answer
Catalytic cracking and steam cracking.
- 5
What must be done to a hydrocarbon before either method of cracking can take place?
Model answer
It must be heated strongly so that it vaporises.
- 6
State one thing that catalytic cracking and steam cracking have in common.
Model answer
Both require the hydrocarbon to be vaporised and heated to a high temperature so that its molecules break apart.
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