Rates of reaction

• Rate of reaction

  Every reaction has a reaction rate, which is the change in the quantities of reactants or products over time
• Measuring the rate of reaction

  1. Observe the changes in the quantities of reactants or products over time

  2. Calculate the rate as the change in concentration over change in time

  3. Concentration is measured in mol dm³ and time can be any convenient measurement
• Concentration


  Chemists use square brackets as shorthand for concentration, e.g. [A] is the concentration of A
• Order of reaction

  The rate of reaction is proportional to the concentration of a particular reactant raised to a power, where the power is the order of reaction for that reactant
• Common orders of reaction

  • Zero order (0)
  • First order (1)
  • Second order (2)
• Zero order reaction


  The rate does not depend on the concentration of the reactant
• First order reaction


  The rate depends on the concentration of the reactant raised to the power of 1
• Second order reaction

  The rate depends on the concentration of the reactant raised to the power of 2
• Rate equation

  The mathematical relationship between the concentrations of the reactants and the reaction rate, e.g. rate = k[A]^x[B]^y
• Rate constant (k)


  The proportionality constant that converts between the rate of reaction and the concentrations and orders
• Overall order of reaction

  The sum of the orders with respect to each reactant
• Initial rate


  The instantaneous rate at the beginning of an experiment when t = 0
• Orders of reaction must be determined experimentally by monitoring how a physical quantity changes over time, they cannot be found directly from the chemical equation