3.1.5 Kinetics

• Collision theory:

  • Reactions can only occur when collisions take place between particles that have sufficient energy
  • Energy needed to break bonds in reactants
• Activation energy: the minimum energy which particles need to collide to start a reaction
• What does the Maxwell-Boltzmann distribution show? the spread of energies that molecules of a gas have at a particular temperature
• Describe how the Maxwell-Boltzman distribution curve will change when you increase temperature:

  • Total area should remain constant
  • Molecules have a wider range of energies than at lower temperatures
  • Both most probable and mean energy have higher energies
• Rate of reaction: The change in concentration of a substance in unit time
• Explain how increasing concentration affect the rate of reaction:

  • More particles per unit volume
  • More frequent collisions
  • Rate of reaction increases
• What is the effect of increasing temperature on the rate of reaction?

  • Particles have increased kinetic energy
  • Many more particles have E >= Ea
  • Many more successful collisions
  • Significant increase in rate of reaction
• How does increasing surface area affect the rate of reaction?

  • More particles exposed
  • More frequent collisions
  • Rate of reaction increases
• Catalyst: Substances that increase reaction rates without getting used up
• How do catalysts work? They provide an alternative route/mechanism with a lower activation energy
• Why does lowering activation energy increase the rate of reaction?

  • more particles have energy above activation energy
  • higher frequency of effective collisions
• Minimum energy in collision theory is called activation energy
• What must particles do in order to react? Collide with sufficient energy (activation energy) and the correct orientation
• Do most collisions result in a reaction? no