Sketching Maxwell Boltzmann Distributions
Kinetics Worksheet
Factors Affecting Rate
A Maxwell Boltzmann distribution for the hydration of ethene is drawn on the axes below. The Y-axis is the number of reactant molecules. Copy it and sketch a new distribution to represent the change and explain what has happened to the rate of reaction.
1. Increase the temperature.
- Particles move faster and have more energy.
- The faster moving particles collide more frequently. You cannot see this on the distribution.
- The increased energy of the particles can be seen on the distribution.
- It increases the rate because the number of particles that have at least the activation energy has increased, increasing the proportion of collisions that are successful.
- These combine to increase the frequency of successful collisions, resulting in a higher rate of reaction.
2. Double the number of molecules in the container.
- Double the particles and double the energy results in the same distribution.
- The same proportion of collisions are successful.
- However, there are more particles, so more frequent collisions result in more frequent successful collisions.
3. Decrease the temperature.
- Particles move slower and have less energy.
- The slower moving particles collide less frequently. You cannot see this on the distribution.
- The decreased energy of the particles can be seen on the distribution.
- It decreases the rate because the number of particles that have at least the activation energy has decreased, decreasing the proportion of collisions that are successful.
- These combine to decrease the frequency of successful collisions, resulting in a lower rate of reaction.
4. Add a catalyst.
- No impact on the energy of the molecules.
- However, more particles have at least the activation energy (greater area under the curve to the right of Ea (cat) than Ea (uncat)).
- This results in more frequent successful collisions.
5. Increase the volume of the container.
- The volume of the container has no impact on the number of particles or the distribution of the energy.
- However, the frequency of the collisions decreases (this cannot be seen in the MB distribution).
- This results in a decreased frequency of successful collisions and therefore rate.
6. Wait some time.
- The reactants get used up over time so the area under the curve decreases.
- Additionally, the temperature decreases due to the reaction being endothermic.
- The average energy and most probable energy are lower.
- These result in less frequent collisions and a lower proportion of the collisions having enough energy.
- These result in a decrease in the frequency of successful collisions, resulting in a decrease in the rate.