Teaching rates of reaction post-16

Rates of reaction covers a broad range of practical, mathematical and conceptual ideas. You can open a window into the sub-microscopic world of reaction kinetics, mechanisms and energetics by applying experimental and empirical data obtained from rate of reaction experiments. This article explores how you can use graphical representations with your students to interrogate reaction dynamics and mechanisms.

The applications of reaction kinetics are critical in many areas. Students will be familiar with the Haber process and how the manipulation of factors can optimise yields. These play a key role in food technology and the making of chemicals and pharmaceuticals. Food producers require accurate information about the rates that foods deteriorate and the way factors such as levels of oxygen, microbes, light and temperature affect these reactions. Furthermore, understanding the timing for drugs to be absorbed into our body and the time for elimination is critical.

What students need to know

To understand the importance of applying reaction kinetics to reveal potential reaction mechanism and energetics profiles, students should have a good grasp of:

• what constitutes a chemical reaction and how we measure and record the rate of a reaction;
• how to represent the changes in a reaction by applying graphical approaches;
• the chemical significance of the slope and intercept of a rate graph;
• the construction and use of straight-line graphs (y=mx+c).

Threshold concepts

Students’ confidence in understanding reaction kinetics requires a good understanding of controlling variables and representing them graphically (seeing how concentration of reactants influences the rate of a reaction); the power series and their manipulation; and the concept of a rate determining step. Download the checklist to get more detail on these concepts and how to present them to students.

Ideas for your teaching

Providing students with real-world applications for reaction rates can be a powerful way to engage them. Choose examples carefully to provide students with interesting opportunities to apply their knowledge and to assess their own depth of understanding. You might need to simplify examples, as in the vitamin C loss box out below, but they still provide a realistic context in which students can apply their rates knowledge.

Another real-world context is the time it takes for our bodies to absorb and eliminate drugs, which is critical for much drug development and research. You can use alcohol as an example to investigate this rate of reaction. Students can sketch graphs for the rate versus concentration for these processes. You can then ask them to write a rate equation.

Assessment

Take-home points

• Use real-life examples of reaction rates to highlight the relevance of the topic and engage students. For example, understanding reaction mechanisms can optimise yields, thereby saving money, or enhance the efficacy of medication.
• Assess students’ understanding by looking at how they apply their knowledge to different questions and scenarios.
• Use demos and videos to cover the practical aspects of the topic with demos or videos.