6-16. kinetics

• • The definition of a catalyst is that it lowers the activation energy by providing an alternative pathway; it does not form part of the products and is therefore not used in the reaction
  • In diagram 1 the letter showing the lower activation energy is P
  • At higher temperatures, the Boltzmann distribution moves down and to the right, showing more particles with a higher energy
  • In diagram 2 the line showing this is line Y

  
• • Higher activation energy means a steeper gradient on a graph of ln k against 1/T 
• Arrhenius plot ( lnk against 1/T)

  1. gradient = -Ea/R
  2. y-intercept is lnA
  3. activation energy is J mol-1
• Rate determining step:

  1. The slowest step in a reaction mechanism is, by definition, the rate-determining step
  2. It is the step with the highest activation energy and can be used to deduce the rate expression
• Rate constant (k):

  1. higher values of k, associated with faster reaction
  2. affected by temperature