WJEC A-Level Chemistry Unit 2 Energy, Rate and Chemistry of Carbon Compounds: a deep dive on thermochemistry, rates, green chemistry and introductory organic chemistry

What Unit 2 actually demands

Unit 2 turns from structure to energy, rate and the first organic chemistry. Examiners want confident enthalpy calculations, sharp Maxwell-Boltzmann reasoning, balanced discussion of chemistry's wider impact, and accurate organic mechanisms. The mechanisms recur throughout A2, so learn them properly now.

This guide ties together the seven topics of the unit, each with a matching dot-point page.

Thermochemistry and rates

Thermochemistry covers enthalpy changes, calorimetry ($q = mc\Delta T$), Hess's law cycles and bond enthalpies. Rates of reaction use collision theory and the Maxwell-Boltzmann distribution to explain how concentration, temperature, surface area and catalysts change the rate by altering the frequency of successful collisions.

The wider impact of chemistry

This distinctive WJEC topic asks you to weigh the benefits and costs of chemical processes, the importance of green chemistry and high atom economy, and the responsible use of finite resources.

Introductory organic chemistry

Organic chemistry begins with naming and isomerism, then the reactions of hydrocarbons (combustion, free-radical substitution, electrophilic addition and polymerisation), halogenoalkanes (nucleophilic substitution and elimination, plus CFCs and ozone), and alcohols and carboxylic acids (oxidation, dehydration and esterification).

Check your knowledge

Attempt these under timed conditions, then check against the solutions.

1. State Hess's law. (1 mark)
2. Write the expression for heat transferred in calorimetry. (1 mark)
3. Use the Maxwell-Boltzmann distribution to explain why temperature increases rate. (3 marks)
4. Explain why a high atom economy is desirable. (2 marks)
5. Describe the mechanism of bromine adding to ethene. (3 marks)
6. Give the conditions for substitution and for elimination of a halogenoalkane. (2 marks)