Key term
OCR GCSE Chemistry A J248
Chemical Reactions
Topic overviewWriting formulae of elements and compoundsBalanced equations, and deducing formulae from ionsState symbols in equationsConservation of mass, and changes of mass in open systemsExothermic and endothermic reactions, and reaction profilesActivation energy and why reactions need itOxidation and reduction in terms of oxygenAcids, alkalis and neutralisationThe ionic equation for neutralisation, and reactions of acidsThe pH scale, acidity and alkalinityMeasuring pH with indicators and pH metersProducts at the electrodes, and molten ionic compoundsElectrolysis of aqueous solutionsInert and non-inert electrodes
Elements, Compounds and Mixtures
Topic overviewPurity, and melting point dataRelative formula mass and empirical formulaeFormulations, and separating mixturesPaper and thin layer chromatographyInterpreting chromatograms and Rf valuesChoosing a purification methodMetals and non-metals in the Periodic TableElectron arrangement and position in the Periodic TableIonic, covalent and metallic bonding comparedDot and cross diagrams, and the limits of modelsReactions, electron arrangement and Mendeleev's tableCarbon's four bonds, and the variety of organic compoundsDiamond, graphite, fullerenes and grapheneBond strength, intermolecular forces and predicting stateBulk properties of ionic, molecular and giant structuresNanoparticles: size and surface area to volumeUses and risks of nanoparticulate materials
Global Challenges
Topic overviewExtracting metals by reduction and by electrolysisThe Haber process and fertiliser productionNitrogen, phosphorus and potassium in agricultureLife cycle assessmentRecycling, and the decisions behind itAlloys, and the corrosion of metalsComparing glass, ceramics, polymers, composites and metalsFunctional groups and homologous seriesPredicting the products of organic reactionsAddition polymerisationDNA and other natural polymersFractional distillation of crude oilThe fractions, and crude oil as a feedstockDependence on hydrocarbons, and crackingChemical cells and fuel cellsThe Earth's early atmosphere, and how oxygen developedThe greenhouse effect, and evidence for climate changeEffects of carbon dioxide and methane, and air pollutantsProducing potable water
Monitoring and Controlling Chemical Reactions
Topic overviewCarrying out an acid–alkali titrationTheoretical mass and percentage yieldAtom economy and its calculationMeasuring the rate of a reaction, and rate graphsFactors affecting rate, and collision theorySurface area and rateCatalysts and how they workReversible reactions and dynamic equilibriumActivation energy, and enzymes as catalysts
Particles
Predicting and Identifying Reactions
Topic overviewGroups 1, 7 and 0, and why they behave as they doTransition metalsPredicting reactivity from the Periodic TableReactivity of metals with water and acidsTests for oxygen, hydrogen, carbon dioxide and chlorineTests for aqueous cations and anionsFlame tests, and identifying metal ionsIdentifying a species from test resultsInstrumental methods of analysis
Particles
The particle model and changes of state
- 3 things to know
- Paper 1
Overview
What the particle model assumes, the arrangement and movement of particles in solids, liquids and gases, melting, freezing, boiling, condensing and sublimation, why melting needs energy and gases compress, what physical and chemical changes are and how to tell them apart, why melting, freezing and dissolving salt are physical while burning magnesium is chemical, and why physical changes reverse easily.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Name the changes of state between solid, liquid and gas, and explain why a gas can be compressed but a solid cannot.
Key term
Name the change of state in which a solid becomes a liquid, and the reverse change.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What does the particle model assume about the particles that make up a substance?
Model answer
It assumes that all substances are made of tiny particles that are constantly moving and are attracted to one another.
- 2
Describe the arrangement and movement of the particles in a solid.
Model answer
They are packed closely together in a regular arrangement and vibrate about fixed positions.
- 3
Describe the arrangement and movement of the particles in a liquid.
Model answer
They are still close together but arranged randomly, and they move around and slide past one another.
- 4
Describe the arrangement and movement of the particles in a gas.
Model answer
They are far apart and arranged randomly, and they move quickly in all directions.
- 5
Name the change of state in which a solid becomes a liquid, and the reverse change.
Model answer
A solid becoming a liquid is melting, and a liquid becoming a solid is freezing.
- 6
Name the change of state in which a liquid becomes a gas, and the reverse change.
Model answer
A liquid becoming a gas is boiling or evaporating, and a gas becoming a liquid is condensing.
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