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### Course: AP®︎/College Chemistry>Unit 5

Lesson 5: Activation energy and reaction rate

# Collision theory and the Maxwell–Boltzmann distribution

Collision theory states that in order for a reaction to occur, reactant particles must collide with enough kinetic energy to overcome the activation energy barrier. A Maxwell–Boltzmann distribution shows the distribution of particle energies at a given temperature and allows for a qualitative estimation of the fraction of particles with sufficient energy to react at that temperature. Created by Jay.

## Want to join the conversation?

• What would the graph look like if the temperature decreased or the pressure changed?
• Why does the dashed line which represents the Ea not pass through the point on the x-axis where the peak is located? Why is it farther right? Didn't the previous videos state that this point determines the Ea?
(1 vote)
• Not sure which “last video” you’re talking about, but it sounds like you’re describing an energy profile. It’s a graph which has a peak but describes something different than the Maxwell–Boltzmann distribution graph.

The energy profile graph has energy (y-axis) versus reaction progress/reaction coordinate (x-axis). It shows the relative energy differences between reactant, product, and transition state particles. The distance between these groups are the activation energy and enthalpy change of the reaction. The activation energy is present in this graph but describes the amount of energy which reactant particles must have to break their bonds in the transition state.

In a Maxwell–Boltzmann distribution graph it has fraction of molecules versus the speed of the molecules. This graph shows that a collection of molecules has a spread of energies, some have higher energy than others. The activation energy is a set energy amount which some molecules have and can react, while other molecules do not have and cannot react. The peak in this graph is simply the mean speed of the molecules, but it has no relation to the activation energy.

So the Maxwell–Boltzmann distribution graph shows the entire population of molecules and the molecules which exceed the activation energy can react and then follow the energy profile graph.

Hope that helps.
(1 vote)
• Hey bro you said that you man bro like yeah so umn yeah....
You uhm made a graph that represents the particle that has higher potential energy can overcome the activation energy barrier. But at you said that particle that has enough kinetic energy bro. So it is little bit confusing bro man bro bro bro yeahhh.
(1 vote)
• For any particles to engage in a successful reaction, they must have a certain minimum amount of energy, known as the activation energy. Essentially it is the amount of energy required to begin breaking the bonds of the reactants.

In a reaction vessel, there many reactant particles with a range of energies. Only a fraction of these particles have sufficient energy equal to the activation energy of a reaction. Those that have as much or more energy than the activation energy are able to react, and those are don’t simply don’t react. Increasing the temperature means more particles than before have sufficient energy to engage in a successful reaction and so you’ll observe an increase in the reaction rate.

Hope that helps.
(1 vote)
• There's that graph again, from to about . It shows "Energy" as the dependent variable, being dependent on "Reaction Progress". I am the learner here, but I can't get this relation, even though I grasp the idea of stability and the energy barrier. The rest of the video makes sense to me, where it discusses Reaction Progress as dependent on Energy, for example at and at .
(1 vote)
• I explained this in a previous question of yours.
(1 vote)
• Why is the transition state so high in energy?