Maxwell-Boltzmann Distributions (Edexcel International AS Chemistry)

Maxwell-Boltzmann distribution curve

• A Maxwell-Boltzmann distribution curve is a graph that shows the distribution of energies at a certain temperature
• In a sample of a gas, a few particles will have very low energy, a few particles will have very high energy, but most particles will have energy in between

The Maxwell-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 

The Maxwell-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