Rate equations

• Equation for rate

  Change in reactants OR product concentration / change in time
• Measuring reaction rate


  Continuous monitoring methods should be used:

  Change in colour: regularly measure absorbance using a colorimeter. Can measure decrease in concentration. For faster reactions, a data logger can be used.

  Gas produced: regularly measure gas in a gas syringe.

  Loss of mass: regularly measure change in mass using a mass balance
• Rate expression

  Tells us about the contribution of species that affects reaction rate.
• Rate expression

  Rate = k[A]^m[B]^n

  • K - reaction constant - varies with temperature
• Order

  Zero:

  • no effect on rate
  • changing conc. of a zero order reactant

  First

  • rate doubles
  • double conc. of first order reactant

  Second

  • rate quadruples : 2^2
  • double conc. of second order reactant
• Overall order

  Sum of each individual order
• Units

  -

  
• Rate expression - K

  k - reaction constant that allows us to equate rate and concentration

  If temp. changes so does K. Rate constant is only fixed at a particular temperature. Only thing that affects K is temperature.

  Larger value fo K - faster the rate of reaction.

  as we increase the temperature, the particles have more kinetic energy and they collide more often. This increases the rate