Pearson International A Level Chemistry Core Practical 10: Determine the activation energy of a reaction

This core practical is part of Pearson's practical-learning programme. The method below is one defensible implementation, not a confidential instruction sheet. Centres may adapt equipment while preserving the scientific purpose, controls, measurements and safety requirements.

Aim and scientific principle

Measure a rate constant or consistent rate proxy at several temperatures and use the Arrhenius relationship.

Begin by translating the title into a testable question. Identify what is deliberately changed, what is measured directly, what is calculated and what must remain controlled. Predict a relationship only after naming the mechanism. A prediction without a reason is weak; a reason without measurable variables cannot guide a practical design.

Apparatus and setup

Use reaction system with measurable rate, thermostatic baths, thermometer or probe, timer, pipettes and data-processing tools. Select every measuring instrument by range and resolution, not by name alone. Draw a labelled scientific setup that shows the working geometry and exactly where readings are taken. Include a control or blank when it distinguishes the target effect from drift, contamination or background response.

Before collecting results, check zero readings, calibration, leaks, alignment or sterility as relevant. Record the instrument resolution beside the first raw-data table. If a digital device displays more digits than its underlying accuracy supports, do not treat every digit as equally certain.

Method

1. Select at least five safe temperatures and equilibrate all reacting solutions before mixing.
2. Measure rate using the same endpoint or fit at each temperature, with repeats.
3. Convert Celsius to kelvin and calculate a rate constant or defensible proportional rate measure.
4. Plot ln k against 1/T and obtain activation energy from the gradient.

Plan the analysis before starting. This reveals whether an additional measurement is needed for a derived quantity and prevents a completed experiment from lacking a mass, length, concentration, background or calibration value. A method should be detailed enough for another trained student to reproduce, while avoiding decorative steps that do not affect validity.

Variables and controls

• Independent variable: absolute temperature.
• Dependent variable: rate constant or a consistent rate proxy.
• Important controls: reactant concentrations and volumes, ionic strength, endpoint, mixing and apparatus.