Kinetics

• Collision Theory:

  • Chemical reactions occur when particles of substances collide
  • Collisions must have energy greater than or equal to the activation energy of the reaction
  • Particle orientation must be correct for a successful reaction
• Reaction Conditions:

  • Impact the collisions of particles
  • Conditions can be altered to provide particles with more energy
  • Changing conditions can increase the likelihood of a collision occurring with sufficient energy to react and increase the rate of reaction
• Maxwell-Boltzmann Distribution:

  • Not all molecules in a substance have the same amount of energy
  • Energies are distributed in a pattern called the Maxwell-Boltzmann distribution
  • Changing reaction conditions alters the shape of the curve, affecting the number of particles with energy greater than the activation energy
  • The total area under the curve represents the total number of molecules in the sample, which must remain constant
• Effect of Temperature:

  • Heating a substance transfers thermal energy, converted to kinetic energy
  • Molecules move faster and further with increased temperature
  • Increased movement leads to more frequent collisions with greater energy
  • Increasing temperature increases the rate of reaction as more collisions of greater energy occur
• Effect of Concentration and Pressure:

  • Increasing concentration leads to molecules being packed closer together, increasing the likelihood of collisions with greater energy
  • Increasing pressure has a similar effect by packing molecules closer together in a smaller volume
  • Both concentration and pressure increase the rate of reaction
• Effect of Catalysts:

  • Catalysts increase the rate of reaction without being used up
  • Provide an alternative reaction path with a lower activation energy
  • The Maxwell-Boltzmann distribution curve remains unchanged in shape, but the position of the activation energy is shifted to the left, allowing a greater proportion of molecules to have sufficient energy to react