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CAIE A-Level Chemistry 8.2.1 Activation Energy

Practise defining activation energy and reading it from reaction pathway diagrams for forward and reverse reactions.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • define EA as the minimum energy required for a collision between reacting particles to be effective
  • measure forward EA from the reactant level to the transition-state maximum on a pathway diagram
  • relate forward and reverse activation energies through the reaction enthalpy and unchanged pathway peak

8.2.1—Activation energy, EA question 1

[Maximum number: 1]

A large excess of 2-bromo-2-methylpropane is added to 0.0010 mol of NaOH(aq), which contains a few drops of phenolphthalein indicator. A stopwatch is started as soon as the substances are mixed. The time taken for the pink colour to disappear is recorded.

The experiment is repeated at different temperatures, keeping all concentrations and volumes of reagents constant.

Table for Question 8.2.1—Activation energy, EA question 1 — CAIE A-Level Chemistry AS

The graph shows the energy distribution of molecules in a sample of 2-bromo-2-methylpropane at 25∘C25^{\circ} \mathrm{C}.
EaE_{\mathrm{a}} represents the activation energy for the reaction.

Figure for Question 8.2.1—Activation energy, EA question 1 — CAIE A-Level Chemistry AS

State the effect of an increase in temperature on EaE_{\mathrm{a}} for this reaction.

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