kinetics

• kinetics is the study of factors which alter the rates of chemical reactions
• the rate of a chemical reaction is monitored by the rate of change in concentration and depends on the concentration of reactions
• A + B -> Products
• if the concentration of A is doubled and the concentration of B is kept constant, the rate of reaction doubles

  this suggest the rate of reaction is directly proportional to the concentration of A so rate a[A]1
• if the rate increases by a factor of 4 when the initial concentration of B is doubled and the concentration of A is kept constant it suggests the rate is directly proportional to the square of concentration B so rate a[B]2
• combined this gives us rate a[A]1[B]2

  this can be rewritten into

  rate = k[A]1[B]2

  this reaction would be in first order with respect to A and second order with respect to B
• k is the rate constant
• the overall order of a reaction is the sum of the power to which the concentrations of the reactants are raised in the rate equation
• overall order = 0 order


  units of k = mol l-1 s-1
• overall order = 1st order


  units of k = s-1
• overall order = 2nd order


  units of k = mol-1 l s-1
• overall order = 3rd order


  units of k = mol-2 l2 s-1
• a reaction mechanism is a set of theoretical steps proposed to account for the reactants being converted into products
• the slowest step is the one which controls the overall rate of reaction and is called the rate-determining step
• a rate equation does not provide definitive proof that it's the reaction mechanism

  an alternative mechanism may give the same rate equation
• no relationship exists between the rate equation and the stochiometric coefficients in a balanced equation