AS AQA Chem Unit 2- The Maxwell-Boltzmann distribution

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Background

The particles in any gas (or solution) are all moving at different speeds, most of which move between slow and very fast. The energy of a particle depends on its speed so the particles also have a range of energies. If a graph is plotted of 'energy' against 'fraction of molecules with that energy', a curve is created called the Maxwell-Boltzmann distribution -this has significant features explaining the distribution of energy amongst the particles;

-No particles have zero energy.

-Most particles have intermediate energies -around the peak of the curve.

-A few have very high energies, in fact there is no upper limit.

-The area under the graph represents the total number of particles.

-There are values for average energy and most probable energy however these are not the same.

Side note: See pages 138-139 of Nelson Thornes AQA Chemistry AS textbook for relevent graphs.

Activation energy, Ea

For a reaction to take place a collision between particles must have enough energy to start breaking bonds. This amount of energy is called activation energy, Ea. If marked on a Maxwell-Boltzmann distribution graph then the area under the graph to the right of the Ea line represents the number of particles with…

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