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OxfordAQA CH04 chemistry: organic 2 and physical 2

Begin with rate equations and Kp, then work through carbonyl chemistry, synthesis and structure determination. Keep the extra OxfordAQA aromatic reactions on your revision list.

CH04 · 90 minutes · 80 marks · 21% of the full A-level

January exam: 13 January 2027. Check the timetable and local starting time.

What to revise for CH04

  • Rate equations, orders, rate constants, Arrhenius graphs and rate-determining steps
  • Mole fractions, partial pressures and Kp
  • Optical isomerism and carbonyl nucleophilic addition
  • Carboxylic acids, esters, acylation and amines
  • Benzene bonding, nitration, sulfonation, Friedel–Crafts alkylation and acylation, and radical chlorine reactions
  • Condensation polymers, amino acids, proteins and cisplatin
  • Organic synthesis, proton and carbon-13 NMR, and chromatography

CH04 assumes CH01 and CH02 knowledge. Include rate equations and Kp in your revision as well as organic chemistry.

Aromatic reactions to include

Revise sulfonation and Friedel–Crafts alkylation alongside nitration and acylation. You also need the radical chlorine reactions of benzene and methylbenzene. With methylbenzene, check whether the reaction happens at the ring or the side chain, and write the conditions with each reaction.

Try CH04 questions

Answer true or false, then read the explanation. Your score counts first answers; any questions you miss come back for a retry.

Questions to work through on paper

Write your answer before opening mine. Check your working and explanation as well as the final answer.

Orders and rate constant

At constant temperature, doubling [A] doubles the rate and doubling [B] quadruples it. At [A] = 0.100 and [B] = 0.200 mol dm⁻³, the rate is 0.00800 mol dm⁻³ s⁻¹. Find the rate equation and k.

Show worked answer

The orders are 1 in A and 2 in B: rate = k[A][B]². k = 0.00800 ÷ (0.100 × 0.200²) = 2.00 dm⁶ mol⁻² s⁻¹. The orders come from the experimental changes, not the overall equation.

Kp and pressure

For N₂O₄(g) ⇌ 2NO₂(g), an equilibrium mixture has partial pressures of 40.0 kPa N₂O₄ and 60.0 kPa NO₂. Calculate Kp and explain the effect of compression at constant temperature.

Show worked answer

Kp = 60.0² ÷ 40.0 = 90.0 kPa. Compression favours N₂O₄ because that side has fewer gas molecules. Kp stays unchanged at constant temperature.

Aromatic reactions to keep separate

Compare Friedel–Crafts alkylation and acylation of benzene. Name the catalyst and describe the difference between the products.

Show worked answer

Both use AlCl₃ to help generate an electrophile and proceed by electrophilic substitution. An alkyl halide attaches an alkyl group; an acyl chloride attaches an acyl group and gives an aromatic ketone. The delocalised ring is restored when H⁺ is lost.

NMR integration ratios

A proton NMR spectrum has signals with integration areas 6 and 4. What is the simplest proton ratio? Does the ratio alone identify the molecule?

Show worked answer

Divide both areas by 2 to get 3:2. The molecule could have 3 and 2 protons in those environments, or a multiple such as 6 and 4. Use the molecular formula, chemical shifts, splitting and other evidence to work out the structure.

More practice

You can use these UK-labelled tools for the topics below. Choose the AQA setting where there’s a choice.

Find UK AQA papers for CH04

About these resourcesMade by Dr T. Smith · Chemistryhelp.co.uk