Maxwell-Boltzmann;
Temperature and Catalysts
Activation Energy
• Collisions only result in a reaction if the
particles collide with enough energy to get
the reaction started. This minimum energy
required is called the activation energy
for the reaction.
• Only a fraction of the total population of a
chemical species will be able to collide
with enough energy to react (E ≥ Ea)
Maxwell-Boltzmann Distribution
• In any system, the particles present will have a very wide range of
energies. For gases, this can be shown on a graph called the
Maxwell-Boltzmann Distribution which is a plot of the number of
particles having each particular energy.
The Maxwell-Boltzmann Distribution
and Activation Energy
• Notice that the
large majority of
the particles don't
have enough
energy to react
when they collide.
• To enable them to
react we either
have to change
the shape of the
curve, or move
the activation
energy further to
the left.
M-B Distribution and Temperature
•
Increasing the temperature:
– increases the average kinetic energy of the gas (slight shift to the right)
– Increases the number of particles whose energy exceeds the activation energy
Catalysts and Activation Energy
• To increase the rate of a reaction you need
to increase the proportion of successful
collisions.
• Catalysts increase the rate of reaction by
providing an alternative way for the
reaction to happen which has a lower
activation energy.
M-B Distribution and Catalysts
Summary
• Maxwell-Boltzmann Energy Distribution Curve
– distribution of a population of a chemical by energy
– Used to show effect of temperature and catalysts on the rate of a
chemical reaction
• Temperature
– changes average kinetic energy of population
– shifts and distorts the M-B Distribution curve
– changes the proportion of particles with Ea.
• Catalysts
– provide alternative pathway with a lower the activation energy
– Ea on M-B curve is shifted left
– no effect on distribution curve itself