AQA AS Chemistry

Revision Notes

1.7.3 Maxwell–Boltzmann Distributions

Maxwell-Boltzmann Distribution Curve - Temperature

Boltzmann distribution curve

  • The Boltzmann distribution curve is a graph that shows the distribution of energies at a certain temperature
  • In a sample of a substance, a few particles will have very low energy, a few particles will have very high energy, and many particles will have energy in between

 

Reaction Kinetics Boltzmann Distribution Curve, downloadable AS & A Level Chemistry revision notes

The Boltzmann distribution curve shows the distribution of the energies and the activation energy

 

  • The graph shows that only a small proportion of molecules in the sample have enough energy for an effective collision and for a chemical reaction to take place

Changes in temperature

  • When the temperature of a reaction mixture is increased, the particles gain more kinetic energy
  • This causes the particles to move around faster resulting in more frequent collisions
  • Furthermore, the proportion of successful collisions increases, meaning a higher proportion of the particles possess the minimum amount of energy (activation energy) to cause a chemical reaction
  • With higher temperatures, the Boltzmann distribution curve flattens and the peak shifts to the right

 

Reaction Kinetics Boltzmann Distribution Curve at higher Temperature, downloadable AS & A Level Chemistry revision notes

The Boltzmann distribution curve at T oC and when the temperature is increased by 10 oC

  • Therefore, an increase in temperature causes an increased rate of reaction due to:
    • There being more effective collisions as the particles have more kinetic energy, making them move around faster
    • A greater proportion of the molecules having kinetic energy greater than the activation energy

Exam Tip

The increase in proportion of molecules having kinetic energy greater than the activation has a greater effect on the rate of reaction than the increase in effective collisions

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