Learner Activity 2: Boltzmann Distribution Curves Part of the ‘Rates of reaction and the Arrhenius equation’ Topic Exploration Pack

Sketch the following graph onto a plain piece of A4 paper

Tasks Label the x and y axes If you calculated the total area under the curve, what would this number be a measure of? What does the line labelled Ea represent? What does the shaded area under the curve represent?

Tasks The graph you have drawn represents the distribution of energies of molecules in a sample of gas. On your diagram, sketch a second distribution curve, for the same gas, but at a lower temperature, label this T2. Comment on the total area under these two curves

Tasks What has happened to the area under the curve to the right of Ea? What is the physical interpretation of this change? How does this relate to the rate of reaction? Now sketch another curve, on the same axes, for the same sample of gases at a higher temperature, label this T3.

Tasks What has happened to the area under the curve to the right of Ea? What is the physical interpretation of this change? How does this relate to the rate of reaction? Explain the effects of catalysts on the rate of reactions. Draw a second vertical line on your graph, and extra shading, to help demonstrate these effect.

Tasks

Answers See previous slide. Total number of particles in the sample. The activation energy of the reaction. The total number of particles with an energy equal to or greater than the activation energy.

Answers See diagram slide. The total areas under the two curves are the same, as the sample has the same number of particles in, regardless of temperature. The area under the curve has decreased, indicating that there are fewer particles with an energy equal to or greater than the activation energy, so there are fewer collisions per second that lead to reaction, so the rate of reaction will decrease.

Answers See diagram slide. The area under the curve has increased, indicating that there are more particles with an energy equal to or greater than the activation energy, so there are more collisions per second that can lead to reaction, so the rate of reaction will increase.

Answers Adding a catalyst provides an alternative reaction pathway, with a lower activation energy, so the Ea line moves to the left. The area under the curve to the right of Ea is therefore greater, indicating more particles have energy equal to or greater than the activation energy, hence the rate of reaction increases.

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