AQA & OCR A · kinetics
Maxwell–Boltzmann distribution simulator and exam questions
Change temperature and activation energy on the simulator, then practise the graph-reading, catalyst and explanation questions that recur in A-level exams.
Interactive graph: change temperature to move the distribution peak and alter the area beyond the activation energy.
Current distribution
300 K reference
Activation energy
Catalysed pathway
At 400 K the teal curve is broader than the 300 K reference. Increase the temperature and watch the peak move right and down while the area beyond Ea increases.
What this visual model represents
The graph uses a normalised Maxwell–Boltzmann-shaped distribution on a relative energy axis. Every temperature curve has the same area. The energy values and reacting fractions are illustrative and do not represent a named gas.
Generated exam practice
Read the curve like an examiner
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What must change when temperature rises?
- The distribution becomes broader and the maximum moves to higher energy.
- The peak becomes lower.
- The total area stays the same when the number of molecules is unchanged.
- A greater proportion of molecules has energy equal to or greater than the activation energy, so successful collisions occur more frequently.
What does a catalyst change?
A catalyst provides an alternative reaction route with a lower activation energy. At the same temperature it does not change the Maxwell–Boltzmann distribution itself. On an exam graph, keep the curve and move the activation-energy threshold to a lower energy.
AQA and OCR A
Both boards use the distribution to explain temperature and catalyst effects. AQA can also ask about most probable and mean energy. For OCR A, those ideas are useful extension rather than core mixed practice.
Pressure is a separate idea. Compressing a gas at constant temperature increases collision frequency, but does not make the molecules' energy distribution shift to higher energies. Do not redraw the Maxwell–Boltzmann curve just because the pressure changed.
Sketch checklist
- y-axis: number of molecules is the safe shared label; AQA questions may also use fraction or proportion
- x-axis: energy
- curve starts at the origin
- one maximum, then a long high-energy tail
- tail approaches the axis rather than turning upwards
Common mark-loss traps
- temperature does not lower Ea
- a catalyst does not move the distribution curve
- higher-temperature curves should have the same total area for the same sample
- "more collisions" alone does not explain the large temperature effect; link the answer to the fraction with E ≥ Ea
- do not swap energy and number of molecules on the axes