Arrhenius graphs are a regular Paper 5 data-analysis question. Work through a student’s iodine clock results: convert to kelvin, work out 1/T, 1/t and ln(1/t), plot every cross yourself on the grid, circle the anomalous point, drag your own line of best fit and read its gradient. Then turn the gradient into Ea and evaluate the method. Every attempt has different results and a different anomaly. Allow about 30 minutes.
Checked: Cambridge 9701 Paper 5, February/March 2023 to May/June 2026. Only the papers in our collection are listed, so the real number may be higher. Question papers are available from Cambridge.
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Why both solutions are brought to the bath temperature before mixing, and why the temperature of the mixture is measured during the run and averaged.
T = θ + 273, then 1/T and 1/t to three significant figures and ln(1/t) to three decimal places, in every row.
Every cross within half a small square, the anomalous point circled, and a straight line of best fit through the other five points.
Two points read from your own line and far apart, the gradient to three significant figures, Ea = −gradient × R in kJ mol⁻¹ with a positive sign, and a value close to the true one.
A reason for the anomaly that fits its direction, the effect of a constant thermometer error on Ea, and a change that really makes the results more reliable.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.