1.5 kinetics

• What is the activation energy, EA, defined as?

  Minimum energy to start reaction
• The Maxwell-Boltzmann energy distribution shows the spread of energies that molecules of a gas or liquid have at a particular temperature
• The Maxwell-Boltzmann energy distribution starts at the origin.
• Why does the energy distribution curve never meet the x-axis?

  No maximum energy for molecules
• The area under the Maxwell-Boltzmann curve represents the total number of particles
• Why do some particles in the Maxwell-Boltzmann distribution have low energies?

  Collisions slow them down
• Only a few particles in the Maxwell-Boltzmann distribution have energy greater than the activation energy.
• Particles can gain energy through collisions
• What happens to the Maxwell-Boltzmann distribution when temperature increases?

  Shifts towards higher energies
• The total area under the Maxwell-Boltzmann curve remains constant when temperature changes.
• At higher temperatures, both the most probable energy and the mean energy shift to higher values
• What is required for a reaction to occur according to collision theory?

  Sufficient collision energy
• What is the minimum energy needed for a reaction to occur called?

  Activation energy
• The rate of reaction is defined as the change in concentration of a substance in unit time.
• When a graph of reactant concentration is plotted against time, the gradient of the curve is the rate of reaction.
• Where is the initial rate of reaction fastest?

  At the start
• What happens to the frequency of effective collisions when concentration increases?

  Increases
• Increasing concentration changes the shape of the Maxwell-Boltzmann energy distribution curve.

  False
• When concentration increases, the area under the Maxwell-Boltzmann curve becomes greater because there are more particles.
• Which factors increase the rate of reaction?

  Temperature, surface area
• In the experiment with sodium thiosulfate and hydrochloric acid, what causes the cross to disappear?

  Cloudy sulfur
• Using the time for the cross to disappear as a measure of reaction rate is an exact calculation.

  False
• Increasing surface area allows successful collisions to occur more frequently.
• How do catalysts increase reaction rates?

  Lower activation energy
• What happens to particle energy at higher temperatures?

  Increases
• At higher temperatures, a significantly bigger proportion of particles have energy greater than the activation energy.
• With a lower activation energy, more particles have energy greater than the EA.