4.5 Energy changes

Unit Summary

This unit aligns with the AQA GCSE Chemistry specification and develops a coherent understanding of the energy changes that accompany chemical reactions. It builds upon prior learning about bonding, structure, and reactivity to explain how the breaking and forming of bonds involve energy transfer between substances and their surroundings, and how these transfers can be harnessed in practical applications such as chemical cells and fuel cells.

Students will learn to distinguish between exothermic and endothermic reactions, recognising that exothermic reactions release energy to the surroundings—often as heat or light—while endothermic reactions absorb energy. Through both theoretical study and practical work, they will investigate heating and cooling effects and explore real-life examples such as self-heating cans, instant cold packs, and combustion reactions, linking these to the underlying energy changes involved in bond breaking and bond formation.

The unit extends understanding to electrochemical systems, where chemical energy is converted into electrical energy. Students will study simple chemical cells and batteries, learning how differences in reactivity between metals can produce a potential difference and drive a flow of electrons through an external circuit. They will also explore the operation of fuel cells, including hydrogen fuel cells, as examples of systems that continuously generate electricity through chemical reactions, offering potential applications in sustainable energy technologies.

Substantive knowledge developed in this unit includes:

The distinction between exothermic and endothermic reactions in terms of energy transfer.

The concept of conservation of energy in chemical reactions.

The relationship between bond breaking (endothermic) and bond making (exothermic).

The interpretation and construction of energy level diagrams (reaction profiles).

The principles of chemical cells, batteries, and fuel cells as examples of chemical reactions producing electrical energy.

How reactivity differences between metals determine the voltage of a cell.

Disciplinary knowledge is strengthened through practical investigations and scientific enquiry. Students will measure temperature changes to classify reactions as exothermic or endothermic, construct and test simple chemical cells using different metal electrodes and electrolytes, and relate their observations to theoretical predictions. These experiences reinforce accurate data collection, analysis, and explanation of evidence in terms of energy changes and redox processes.

Assessment for Learning (AfL) strategies are embedded throughout, using retrieval practice to reinforce key concepts, diagnostic questioning to address misconceptions (for example, confusing energy with temperature), and scaffolded writing tasks to develop confidence in describing and interpreting energy changes and voltage production.

Real-world links are emphasised throughout, helping students understand how energy changes underpin technologies such as batteries, hydrogen fuel cells, and renewable energy systems. These contexts highlight the importance of chemistry in addressing global challenges such as sustainable energy storage and low-carbon transport.

Designed to be accessible and progressive, this unit enables students to describe, represent, and quantify energy changes in chemical reactions, while also understanding how these principles are applied in chemical and electrochemical energy systems. By the end of the unit, learners will be able to interpret energy profiles, explain the operation of cells and fuel cells, and appreciate the central role of energy transformations in modern science and technology.