Key term
OCR GCSE Combined Science Chemistry J250
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 structures
Global Challenges
Topic overviewExtracting metals by reduction and by electrolysisLife cycle assessmentRecycling, and the decisions behind itFractional distillation of crude oilThe fractions, and crude oil as a feedstockDependence on hydrocarbons, and crackingThe 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
Particles
Monitoring and Controlling Chemical Reactions
Catalysts and how they work
- 3 things to know
- Paper 4 (Chemistry)
Overview
What a catalyst is, why its mass is unchanged and it sits above the arrow, why catalysts are specific and used in industry, and the catalysts for hydrogen peroxide, ammonia and sulfuric acid.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Describe how you could show experimentally that a substance added to a reaction acted as a catalyst.
Key term
Name a metal used as the catalyst in a car's catalytic converter.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is a catalyst?
Model answer
It is a substance that increases the rate of a reaction without being used up or chemically changed by the end of it.
- 2
Is a catalyst used up during a reaction, and what does this mean for its mass at the end?
Model answer
No, it is not used up, so the same mass of catalyst can be recovered at the end and used again.
- 3
Does a catalyst appear as a reactant in the balanced equation for a reaction?
Model answer
No, because it is not consumed; it is usually written above the arrow instead.
- 4
Are catalysts general or specific in their action?
Model answer
They are specific, so a catalyst that works for one reaction will usually have no effect on a different one.
- 5
Does adding a catalyst change the amount of product a reaction eventually makes?
Model answer
No, it changes only how quickly the product is made; the final amount is the same.
- 6
Give two reasons why catalysts are used so widely in industry.
Model answer
They allow a useful rate at a lower temperature or pressure, which saves energy and money, and they increase the amount of product made per day from the same plant.
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