WJEC A Level Chemistry
WJEC A Level Chemistry Unit 2: Energy, Rate and Chemistry of Carbon Compounds Exam Questions
Free WJEC A Level Chemistry exam questions for Unit 2: Energy, Rate and Chemistry of Carbon Compounds, with a mark scheme for every pack. Covers thermochemistry, Hess's law, bond enthalpies, rates and catalysts, sustainability, organic naming, hydrocarbons, halogenoalkanes, alcohols, carboxylic acids and instrumental analysis.
Unit 2: Energy, Rate and Chemistry of Carbon Compounds exam questions
8 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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A-Level Chemistry Flashcards for 2027 Onwards
Every answer is written in mark scheme wording, so you learn exactly what examiners give marks for. Then test yourself with the questions on this page.
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About WJEC A Level Chemistry Unit 2: Energy, Rate and Chemistry of Carbon Compounds
Unit 2 is the second AS unit of the WJEC A Level Chemistry course and contributes to the full A Level grade. It covers thermochemistry, rates of reaction, the wider impact of chemistry, organic nomenclature and isomerism, alkanes and alkenes, halogenoalkanes, alcohols and carboxylic acids, and instrumental analysis using mass, IR and NMR spectra. This organic and physical base is developed further in Unit 3 (kinetics and energetics) and Unit 4 (organic chemistry and analysis). Examiners frequently test enthalpy calculations with evaluation of errors, mechanisms with curly arrows, tests for functional groups and the identification of compounds from spectral data.
What you need to know
- 2.1 Thermochemistry Enthalpy change definitions under standard conditions, calorimetry with Q = mc delta T, Hess's law cycles using formation and combustion data, and average bond enthalpies.
- 2.2 Rates of reaction Collision theory, activation energy and the Boltzmann distribution; how concentration, pressure, temperature, surface area and catalysts affect rate; measuring rate by gas collection, mass loss or colorimetry.
- 2.3 The wider impact of chemistry Sustainable chemistry, atom economy, use of catalysts and renewable feedstocks, and the environmental impact of fuels including carbon dioxide emissions and climate change.
- 2.4 and 2.5 Organic compounds and hydrocarbons Naming, functional groups, structural and E/Z isomerism. Alkanes: combustion and radical substitution. Alkenes: electrophilic addition, bromine water test and addition polymers.
- 2.6 Halogenoalkanes Nucleophilic substitution with OH-, CN- and NH3; elimination with ethanolic KOH; hydrolysis rates linked to C to X bond enthalpies; environmental impact of CFCs on the ozone layer.
- 2.7 and 2.8 Alcohols, acids and analysis Oxidation of primary and secondary alcohols, dehydration to alkenes, esterification; reactions of carboxylic acids. Identify compounds using mass spectra, IR spectra and NMR.
Common mistakes in Unit 2: Energy, Rate and Chemistry of Carbon Compounds
- Leaving out the minus sign in exothermic delta H values.
- Saying temperature increases rate mainly because particles collide more often. The main reason is more particles have energy at least equal to the activation energy.
- Drawing curly arrows from hydrogen atoms or positive charges in mechanisms.
- Forgetting that tertiary alcohols are not oxidised by acidified dichromate.
- Confusing the broad O to H absorption in carboxylic acids with the C to H absorption near 2900 cm-1.
Try three Unit 2: Energy, Rate and Chemistry of Carbon Compounds exam-style questions
1. Use the data to calculate the enthalpy change for C2H4(g) + H2(g) gives C2H6(g). Delta fH: C2H4 = +52, C2H6 = -85 kJ mol-1. (2 marks)
Show the mark scheme answer
Delta H = sum delta fH products - sum delta fH reactants = -85 - (+52); = -137 kJ mol-1.
2. Draw the mechanism for the reaction of propene with bromine. (3 marks)
Show the mark scheme answer
Induced dipole on Br2 with arrow from C=C to delta positive Br and arrow from Br to Br bond to the other Br; carbocation intermediate with Br- lone pair attacking C+; product 1,2-dibromopropane.
3. Explain why 1-iodobutane hydrolyses faster than 1-chlorobutane. (2 marks)
Show the mark scheme answer
The C to I bond is weaker (lower bond enthalpy) than the C to Cl bond; so it is broken more easily and the reaction is faster.
Unit 2: Energy, Rate and Chemistry of Carbon Compounds FAQs
What does WJEC A Level Chemistry Unit 2 cover?
It covers thermochemistry, rates of reaction, the wider impact of chemistry, organic naming and isomerism, hydrocarbons, halogenoalkanes, alcohols and carboxylic acids and instrumental analysis.
Does WJEC Unit 2 count towards the A Level?
Yes. It is an AS unit within the unitised WJEC A Level, so it contributes to the final A Level grade as well as the AS.
How do I revise organic chemistry for Unit 2?
Make a reaction map for alkanes, alkenes, halogenoalkanes, alcohols and acids with reagents and conditions, and practise drawing each mechanism until every arrow is in the right place.
