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
- 6 subtopics
- 18 things to know
- Paper 4 (Chemistry)
What Monitoring and Controlling Chemical Reactions covers
Monitoring and Controlling Chemical Reactions is examined in Paper 4 (Chemistry). It covers measuring the rate of a reaction and rate graphs; factors affecting rate and collision theory; surface area and rate; catalysts and how they work; reversible reactions and dynamic equilibrium; and activation energy and enzymes as catalysts.
Where it is assessed
Paper 4 (Chemistry)
Combined Science A, Paper 4 (Chemistry): 1 hour 10 minutes, 60 marks, 16.7% of the qualification.
Check the OCR specification ↗The 6 subtopics
Each one has its own page.
- Measuring the rate of a reaction, and rate graphsWhat rate means, following a reaction with a gas syringe, a balance, a disappearing cross, a colorimeter or a pH probe, the units of rate, and reading the gradient of a rate graph.Open →
- Factors affecting rate, and collision theoryHow temperature, concentration, pressure and surface area affect rate, why concentration changes the speed but not the amount of product, the rough doubling for each 10 °C rise, how rate changes during a reaction, the two conditions for a successful collision, explaining each factor with collision theory and activation energy, reading rate ∝ 1/t, and planning, evaluating and improving the sodium thiosulfate investigation.Open →
- Surface area and rateHow breaking a solid up raises its surface area to volume ratio, why powders react faster, the cube calculations, the flour dust hazard, and comparing the graphs for powder and lumps.Open →
- Catalysts and how they workWhat 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.Open →
- Reversible reactions and dynamic equilibriumWhat a reversible reaction is and its symbol, why the reverse of an exothermic reaction is endothermic, heating hydrated copper(II) sulfate and testing for water, heating ammonium chloride, the nitrogen and hydrogen that form ammonia, what dynamic equilibrium and a closed system are, what the position of equilibrium means, and how the forward and reverse rates change until equilibrium is reached.Open →
- Activation energy, and enzymes as catalystsHow a catalyst gives a pathway with a lower activation energy, reaction profiles for catalysed reactions, why lowering the activation energy speeds a reaction, calculating activation energies and energy changes from profiles, what enzymes are and why organisms need them, denaturing by heat and pH, enzyme specificity, uses in brewing and washing powders, and how enzymes compare with metal catalysts.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
How can an acid-consuming reaction be followed without collecting gas, what units does a rate take, and what does a rate graph's steepness show?
Key term
How does powdering a solid change the rate, which factor applies just to gases, what must a collision have, and why does heating help?
Key term
Explain why a powdered solid reacts faster than the same mass of the solid in one large lump.
Key term
Explain why only a small mass of catalyst is needed to convert a very large mass of reactant.
Key term
What symbol is used in an equation to show that a reaction is reversible?
Key term
Describe how the reaction profile for a catalysed reaction differs from that of the same reaction without a catalyst.
Key term
Describe the effect of raising the temperature on the rate of a reaction.
Key term
Which particles of a solid reactant are able to take part in a reaction with a solution?
Key term
Describe how you could show experimentally that a substance added to a reaction acted as a catalyst.
Key term
How is anhydrous copper(II) sulfate used as a test for water?
Key term
Explain why lowering the activation energy makes a reaction faster.
Key term
In general terms, what two quantities can be followed over time to measure the rate of a reaction?
Key term
Describe the effect of increasing the concentration of a reactant in solution on the rate of a reaction.
Numbers
A cube of solid has sides of 3 cm. Calculate its surface area, its volume and its surface area to volume ratio.
Key term
Name a metal used as the catalyst in a car's catalytic converter.
Key term
Name the two gases that combine reversibly to make ammonia.
Key term
A reaction profile shows the reactants at 100 kJ/mol, the peak at 180 kJ/mol and the products at 40 kJ/mol. Calculate the activation energy and the overall energy change.
Take Monitoring and Controlling Chemical Reactions further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Dynamic equilibrium vs Reversible reaction
Dynamic equilibrium: closed-system state where forward and reverse rates are equal. Reversible reaction: products can react together to re-form the original reactants.
Questions from this topic
Each one with the model answer underneath.
- 1
What is meant by the rate of a chemical reaction?
Model answer
It is the amount of reactant used up, or of product formed, in a given time.
- 2
In general terms, what two quantities can be followed over time to measure the rate of a reaction?
Model answer
How quickly a reactant is used up, or how quickly a product is formed.
- 3
Suggest a method for measuring the rate of a reaction that gives off a gas, using a gas syringe.
Model answer
Connect the flask to a gas syringe and record the volume of gas collected at fixed time intervals, such as every 10 seconds.
- 4
Suggest how a balance can be used to measure the rate of a reaction that releases a gas, and explain why the mass changes.
Model answer
Stand the open flask on a balance and record the mass at fixed intervals; the mass falls because the gas produced escapes from the flask.
- 5
Suggest a method for measuring the rate of a reaction that produces a cloudy precipitate.
Model answer
Stand the flask over a marked cross and time how long it takes for the cross to become invisible through the mixture, as happens when sodium thiosulfate reacts with hydrochloric acid.
- 6
Suggest how the rate of a reaction in which the colour of the solution changes could be followed.
Model answer
Use a colorimeter to measure how much light the solution absorbs at set times, since the reading changes as the coloured substance is used up or formed.
What is inside Levo
Six ways to work the same material.
Monitoring and Controlling Chemical Reactions revision questions
- What does Monitoring and Controlling Chemical Reactions cover in OCR GCSE Combined Science Chemistry?
- 6 subtopics: measuring the rate of a reaction, and rate graphs, factors affecting rate, and collision theory, surface area and rate, catalysts and how they work, reversible reactions and dynamic equilibrium and activation energy, and enzymes as catalysts. Each one has its own page with questions and model answers.
- How is Monitoring and Controlling Chemical Reactions organised?
- By the OCR J250 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Monitoring and Controlling Chemical Reactions, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
Or £46 a year, about £3.83 a month. Cancel anytime.