Initial rates experiments

• The initial rate of a reaction is the rate right at the start of the reaction

• In the initial rates method, the time taken for a set amount of product to form at the beginning of the reaction is measured

• The experiment can be repeated, using different initial concentrations of one of the reactants

• The following assumptions are made when using the initial rates method:

  • The concentration of other reactants isn’t changing significantly. This is usually done by adding a large excess of the other reactants

  • The temperature stays constant

  • The reaction has not proceeded to far when measurements are taken

• Initial rate = amount of reactant used or product formed / time

• The initial rate can also be estimated from a concentration-time graph

• The initial rate is the gradient when t = 0

Clock reactions

• A clock reaction has an easily observable end point, usually a colour change, that indicates when the desired amount of product has formed

• The quicker the clock reaction finishes, the faster the initial rate of the reaction