Key term
OCR GCSE Combined Science Chemistry J250
Chemical Reactions
Topic overviewWriting formulae of elements and compoundsBalanced equations, and deducing formulae from ionsIonic equations, and state symbolsThe mole and the Avogadro constantConservation of mass, and changes of mass in open systemsStoichiometry, and calculating reacting massesExothermic and endothermic reactions, and reaction profilesActivation energy, and bond energy calculationsOxidation and reduction, by oxygen and by electronsAcids, alkalis and neutralisationThe ionic equation for neutralisation, and reactions of acidsDilute and concentrated, weak and strongThe pH scale, and hydrogen ion concentrationpH as a factor of ten, and measuring pHProducts 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 electrolysisBiological methods of metal extractionLife 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
Topic overviewMass of solute, concentration and dilution calculationsMeasuring the rate of a reaction, and rate graphsFactors affecting rate, and collision theorySurface area and rateCatalysts and how they workReversible reactions and dynamic equilibriumChanging the conditions of an equilibriumActivation energy, and enzymes as catalysts
Particles
Monitoring and Controlling Chemical Reactions
- 8 subtopics
- 24 things to know
- Paper 10 (Chemistry)
What Monitoring and Controlling Chemical Reactions covers
Monitoring and Controlling Chemical Reactions is examined in Paper 10 (Chemistry), except the mass of a solute and concentration, which the specification places in Topic C3 and examines in Paper 9 (Chemistry). It covers the mass of a solute and concentration calculations; 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; changing the conditions of an equilibrium; and activation energy and enzymes as catalysts.
Where it is assessed
Paper 10 (Chemistry)
Combined Science A, Paper 10 (Chemistry): 1 hour 10 minutes, 60 marks, 16.7% of the qualification.
Check the OCR specification ↗The 8 subtopics
Each one has its own page.
- Mass of solute, concentration and dilution calculationsHow the mass of solute and the volume of solution decide the concentration, the effect of adding water, concentration in g/dm³, and calculating masses, volumes and concentrations in mol/dm³ for sodium and potassium hydroxide solutions, including a dilution.Open →
- 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 →
- Changing the conditions of an equilibriumLe Chatelier’s principle, and the effect on the position of equilibrium of changing concentration, removing a product, raising or lowering the temperature, and changing the pressure, with the compromise conditions for ammonia and sulfur trioxide.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.
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For the exothermic equilibrium 2SO₂ + O₂ ⇌ 2SO₃, why is a moderately high temperature used and what does raising the pressure do?
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How does the mass of solute dissolved affect the concentration of a solution when the volume is fixed?
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Describe the effect of raising the temperature on the rate of a reaction.
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Explain why a powdered solid reacts faster than the same mass of the solid in one large lump.
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Explain why only a small mass of catalyst is needed to convert a very large mass of reactant.
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What symbol is used in an equation to show that a reaction is reversible?
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Describe how the reaction profile for a catalysed reaction differs from that of the same reaction without a catalyst.
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Water is added to a solution without adding any more solute. Explain what happens to the concentration.
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In general terms, what two quantities can be followed over time to measure the rate of a reaction?
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Describe the effect of increasing the concentration of a reactant in solution on the rate of a reaction.
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Which particles of a solid reactant are able to take part in a reaction with a solution?
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Describe how you could show experimentally that a substance added to a reaction acted as a catalyst.
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How is anhydrous copper(II) sulfate used as a test for water?
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State the principle used to predict how the position of an equilibrium responds to a change in conditions.
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Explain why lowering the activation energy makes a reaction faster.
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State the relationship between the mass of solute, the volume of solution and the concentration in g/dm³.
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Suggest how a balance can be used to measure the rate of a reaction that releases a gas, and explain why the mass changes.
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Describe the effect of increasing the pressure on a reaction between gases.
Numbers
A cube of solid has sides of 3 cm. Calculate its surface area, its volume and its surface area to volume ratio.
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Name a metal used as the catalyst in a car's catalytic converter.
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Name the two gases that combine reversibly to make ammonia.
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Predict the effect of increasing the concentration of a reactant on the position of an equilibrium.
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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
How does the mass of solute dissolved affect the concentration of a solution when the volume is fixed?
Model answer
Concentration is directly proportional to the mass of solute, so doubling the mass doubles the concentration.
- 2
Water is added to a solution without adding any more solute. Explain what happens to the concentration.
Model answer
The concentration falls, because the same mass of solute is now spread through a larger volume of solution.
- 3
State the relationship between the mass of solute, the volume of solution and the concentration in g/dm³.
Model answer
Concentration in g/dm³ equals the mass of solute in grams divided by the volume of the solution in dm³.
- 4
Calculate the mass of sodium hydroxide, relative formula mass 40, needed to make 250 cm³ of solution of concentration 2.00 mol/dm³.
Model answer
2.00 × 0.250 = 0.500 mol, and 0.500 × 40 = 20.0 g, given to 3 significant figures.
- 5
Calculate the mass of potassium hydroxide, relative formula mass 56, in 50.0 cm³ of solution of concentration 0.100 mol/dm³.
Model answer
0.100 × 0.0500 = 0.00500 mol, and 0.00500 × 56 = 0.280 g, given to 3 significant figures.
- 6
What volume of a solution of concentration 0.500 mol/dm³ contains 0.100 mol of solute?
Model answer
0.100 ÷ 0.500 = 0.200 dm³, which is 200 cm³, given to 3 significant figures.
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?
- 8 subtopics: mass of solute, concentration and dilution calculations, 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, changing the conditions of an 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.
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