Rate Equations

• rate graph of 0 order

  • no effect on the rate of reaction
  • no relationship between the concentration of the reactant and the rate of reaction

  
• rate graph of 1st order

  • this shows that there is a direct effect on the rate of the reactant
  • the concentration of the reactant is directly proportional to the rate of the reaction

  
• rate graph of 2nd order

  • there is a direct effect on the rate of the reaction
  • there is a quadratic (squared) relationship between the concentration of the reactant and the rate of the reaction

  
• Rate Expression

  • in the example of A + B -> C + D, where m and n are orders (respectively, wrt A and wrt B)
  • the total rate = m + n
  • $rate=$$k\left[A\right]^m\left[B\right]^n$
  • order can only be determined experimentally
• Order

  the amount by which each species affects the rate of the reaction
• Rate Determining Step

  • as many steps occur in several steps, the slowest step determines the overall rate of reaction and is called the “rate determining step” (RDS)
  • only the reactants which occur in the RDS appear in the rate equation
• Arrhenius

  • $\ln\ k=$$-\frac{Ea}{RT}+$$\ln A$
  • $k=$$Ae^{-\frac{Ea}{RT}}$
  • the fraction of molecules with E > Ea is:
  • $e^{-\frac{Ea}{RT}}$