5.6 Rates of reaction

Unit Summary

This unit is aligned with the AQA GCSE Combined Science: Trilogy specification and is designed for flexible delivery. It is structured with the assumption that learners build progressively on knowledge and scientific enquiry skills developed in earlier units and key stages.

The unit integrates both substantive knowledge (core scientific ideas) and disciplinary knowledge (working scientifically), ensuring that students learn key principles through context-based investigations and real-world applications. Central to this unit is the understanding that chemical reactions can occur at vastly different rates. While reactivity of substances plays a role, there are numerous variables—such as temperature, concentration, surface area, and catalysts—that can be manipulated to either increase or decrease the rate of reaction.

Students are introduced to collision theory to explain how these factors affect the frequency and energy of particle collisions. Practical work is embedded throughout, enabling learners to develop experimental skills through investigations that measure the rate of reaction using changes in mass, volume of gas produced, or changes in colour or turbidity.

The unit also links with ideas from energy changes in chemical reactions and the concept of reversible reactions, preparing students for further learning in equilibrium and chemical industry contexts. These links are made explicit: students examine how reaction conditions can be adjusted to maximise yield of desired products in reversible reactions, as well as the trade-offs required to balance rate, yield, and energy efficiency—key considerations in industrial chemistry.

This knowledge is framed through the lens of careers in chemical engineering and industrial chemistry, highlighting how scientists apply this understanding in optimisation processes to ensure efficient, large-scale production. Students explore the compromises that professionals must make between yield, time, and energy demands, promoting a deeper appreciation of the complexities of industrial reaction design.

Throughout the unit, working scientifically is emphasised. Pupils plan and carry out controlled experiments, identify variables, record observations, and analyse data to draw conclusions about reaction conditions. Scaffolds are provided to ensure accessibility for all learners, with careful attention paid to addressing misconceptions around particle behaviour, catalyst function, and the meaning of ‘rate’.

To support long-term learning and progression, a variety of Assessment for Learning (AfL) strategies are embedded in each lesson. These include retrieval practice, diagnostic questioning, and structured discussion tasks that promote metacognition, reinforce key concepts, and encourage self-assessment.

In addition to meeting National Curriculum requirements, this unit extends learning through real-world connections, particularly in relation to environmental sustainability, industrial efficiency, and the economic and societal relevance of chemistry. Students are encouraged to consider how their scientific learning links to the wider world of work, innovation, and problem-solving.