Kinetics

• What is the definition of activation energy (EA)?

  It is the minimum energy which particles need to collide to start a reaction.
• What does the Maxwell-Boltzmann energy distribution illustrate?

  It shows the spread of energies that molecules of a gas or liquid have at a particular temperature.
• What are the key features of the Maxwell-Boltzmann energy distribution curve?

  • Passes through the origin (no molecules with zero energy)
  • Never meets the x-axis (no maximum energy)
  • Mean energy is not at the peak of the curve
  • Area under the curve represents total number of particles
• Why do only a few particles have energy greater than the activation energy (EA)?

  Because most molecules have energies between the extremes, and the distribution is not symmetrical.
• How can a reaction go to completion if few particles have energy greater than EA?

  Particles can gain energy through collisions.
• What happens to the energy distribution as temperature increases?

  The distribution shifts towards having more molecules with higher energies.
• What remains constant when the temperature increases in the Maxwell-Boltzmann distribution?

  The total area under the curve remains constant because the total number of particles is constant.
• How does increasing temperature affect the Emp and mean energy of particles?

  Both the Emp and mean energy shift to higher energy values.
• What is the definition of the rate of reaction?

  It is the change in concentration of a substance in unit time.
• What is the usual unit for measuring the rate of reaction?

  mol dm^-3s^-1
• How can the rate of reaction be determined from a concentration vs. time graph?

  The gradient of the curve represents the rate of reaction.
• What is the initial rate of a reaction?

  It is the rate at the start of the reaction where it is fastest.
• How can reaction rates be calculated from graphs?

  By drawing a tangent to the curve at different times and calculating the gradient of the tangent.
• What effect does increasing concentration have on reaction rates?

  It increases the frequency of effective collisions due to more particles per unit volume.
• How does increasing concentration affect the shape of the energy distribution curve?

  The shape does not change, but the curves will be higher and the area under the curves will be greater.
• What happens to the number of molecules with energy greater than EA when concentration increases?

  More molecules have energy greater than EA, although not a greater proportion.
• What factors affect the rate of reaction?

  • Higher concentration
  • Higher temperature
  • Increased surface area
  • Presence of catalysts
• How does increasing surface area affect reaction rates?

  It causes successful collisions to occur more frequently, increasing the rate of the reaction.
• What is the definition of a catalyst?

  A catalyst increases reaction rates without getting used up.
• How do catalysts increase reaction rates?

  By providing an alternative route or mechanism with a lower activation energy.
• What is the effect of lower activation energy on the frequency of effective collisions?

  More particles will have energy greater than EA, leading to a higher frequency of effective collisions.
• How does increasing temperature affect particle collisions?

  Particles collide more frequently and more often with energy greater than the activation energy.
• What happens to the proportion of particles with energy greater than the activation energy as temperature increases?


  A significantly bigger proportion of particles have energy greater than the activation energy.
• What is the overall effect of increasing temperature on reaction rates?

  • Increases the energy of particles
  • Increases the frequency of collisions
  • Increases the frequency of successful collisions
• What is the difference in activation energy between catalyzed and uncatalyzed reactions?

  • Catalyzed reactions have lower activation energy
  • More particles have energy greater than EA in catalyzed reactions
  • Higher frequency of effective collisions in catalyzed reactions