OCR 2016 Learner Activity 2 Boltzmann Distribution Curves

Learner Activity 2: Boltzmann Distribution Curves Part of the ‘Rates of reaction and the Arrhenius equation’ Topic Exploration Pack © OCR 2016

Sketch the following graph onto a plain piece of A 4 paper © OCR 2016

Tasks 1. Label the x and y axes 2. If you calculated the total area under the curve, what would this number be a measure of? 3. What does the line labelled Ea represent? 4. What does the shaded area under the curve represent? © OCR 2016

Tasks 5. 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 T 2. 6. Comment on the total area under these two curves © OCR 2016

Tasks 7. 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? 8. Now sketch another curve, on the same axes, for the sample of gases at a higher temperature, label this T 3. © OCR 2016

Tasks 9. 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? 10. 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. © OCR 2016

Tasks © OCR 2016

Answers 1. See previous slide. 2. Total number of particles in the sample. 3. The activation energy of the reaction. 4. The total number of particles with an energy equal to or greater than the activation energy. © OCR 2016

Answers 5. See diagram slide. 6. The total areas under the two curves are the same, as the sample has the same number of particles in, regardless of temperature. 7. 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. © OCR 2016

Answers 8. See diagram slide. 9. 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. © OCR 2016

Answers 10. 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. © OCR 2016

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