Edexcel International GCSE Chemistry
Edexcel International GCSE Chemistry Section 3: Physical Chemistry Exam Questions
Free Edexcel International GCSE Chemistry exam questions for Section 3: Physical Chemistry, with a mark scheme for every pack. Covers energetics and enthalpy changes, calorimetry, bond energies, rates of reaction and collision theory, catalysts, reversible reactions and equilibria.
Section 3: Physical Chemistry exam questions
4 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel International GCSE Chemistry Section 3: Physical Chemistry
Section 3 of Edexcel International GCSE Chemistry (4CH1) covers energetics, rates of reaction, and reversible reactions and equilibria. You learn to measure and calculate enthalpy changes using simple calorimetry and bond energies, draw energy level diagrams, investigate how surface area, concentration, temperature and catalysts affect the rate of a reaction, and explain these results using collision theory. You then study reversible reactions and how changing conditions affect the position of a dynamic equilibrium. It is assessed on both papers, with bold content on Paper 2 only. Calorimetry calculations, practical descriptions and explanations of rate graphs are popular exam questions.
What you need to know
- Exothermic and endothermic Exothermic reactions give out heat energy (ΔH negative); endothermic reactions take in heat energy (ΔH positive). Represent them on energy level diagrams.
- Calorimetry Measure temperature changes for combustion, displacement, dissolving and neutralisation. Heat energy change Q = m x c x ΔT, where m is the mass of water or solution and c is 4.2 J/g/°C. Molar enthalpy change ΔH = -Q / n, usually in kJ/mol.
- Bond energies Breaking bonds is endothermic and making bonds is exothermic. ΔH = sum of bonds broken minus sum of bonds made.
- Rates of reaction Investigate the effects of surface area (marble chips and acid), concentration, temperature (sodium thiosulfate and acid) and catalysts (hydrogen peroxide decomposing with a catalyst) on rate. Rate can be followed by gas volume, mass loss or time for a precipitate to form.
- Collision theory and catalysts Increasing concentration and surface area increase collision frequency; increasing temperature increases collision frequency and the proportion of particles with energy at least equal to the activation energy. A catalyst provides an alternative pathway with lower activation energy, shown on a reaction profile.
- Reversible reactions and equilibria Examples include heating ammonium chloride and dehydrating hydrated copper(II) sulfate. In a closed system dynamic equilibrium is reached when forward and backward rates are equal. Changes in temperature and pressure shift the position of equilibrium; a catalyst does not change the position.
Common mistakes in Section 3: Physical Chemistry
- Using the mass of the solid reactant instead of the mass of the water or solution in Q = mcΔT.
- Forgetting the negative sign for an exothermic ΔH.
- Forgetting to convert joules to kilojoules when giving ΔH in kJ/mol.
- Saying increasing temperature only increases the number of collisions. It also increases the energy of collisions so more exceed the activation energy.
- Saying a catalyst shifts equilibrium. It speeds up forward and backward reactions equally.
Try three Section 3: Physical Chemistry exam-style questions
1. 50 g of solution increases in temperature by 6.0 °C when 0.025 mol of acid is neutralised. Calculate the molar enthalpy change. (c = 4.2 J/g/°C) (3 marks)
Show the mark scheme answer
Q = 50 x 4.2 x 6.0 = 1260 J; ΔH = -1260 / 0.025 = -50 400 J/mol; = -50.4 kJ/mol.
2. Explain, using collision theory, why increasing the concentration of an acid increases the rate of its reaction with magnesium. (2 marks)
Show the mark scheme answer
More acid particles in the same volume; so more frequent collisions (more collisions per second).
3. For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), explain the effect of increasing pressure on the amount of SO3 at equilibrium. (2 marks)
Show the mark scheme answer
Amount of SO3 increases; equilibrium shifts to the side with fewer moles of gas (3 to 2).
Section 3: Physical Chemistry FAQs
What does Edexcel International GCSE Chemistry Section 3 cover?
It covers energetics, including calorimetry and bond energy calculations, rates of reaction and collision theory, catalysts, reversible reactions and dynamic equilibrium.
Which paper is Section 3 examined on?
It is assessed on both Paper 1 and Paper 2, with content shown in bold in the specification assessed on Paper 2 only.
What equations do I need for Section 3?
Learn Q = m x c x ΔT (with c = 4.2 J/g/°C for water), ΔH = -Q / n, and ΔH = bonds broken minus bonds made. Check units: Q is in joules, ΔH is usually in kJ/mol.
