Order of reaction from initial rate

• The?progress?of the reaction can be followed by measuring the?initial?rates?of the reaction using various?initial concentrations?of each reactant
• These rates can then be plotted against time in a rate-time graph
• In a?zero-order?reaction the rate doesn’t depend on the concentration of the reactant
  • The rate of the reaction therefore remains constant throughout the reaction
  • The graph is a?horizontal line
  • The rate equation is?rate =?k

   

Rate-concentration graph of a zero-order reaction

• In a?first-order?reaction the rate is directly proportional to the concentration of a reactant
  • The rate of the reaction increases as the concentration of the reactant increases
  • This means that the rate of the reaction decreases as the concentration of the reactant decreases when it gets used up during the reaction
  • The graph is a?straight line
  • The rate equation is?rate =?k?[A]

   

Rate-concentration graph of a first-order reaction

• In a?second-order?reaction, the rate is directly proportional to the square of concentration of a reactant
  • The rate of the reaction increases more as the concentration of the reactant increases
  • This means that the rate of the reaction decreases more as the concentration of the reactant decreases when it gets used up during the reaction
  • The graph is a?curved line
  • The rate equation is?rate =?k?[A]2

   

Rate-concentration graphs of a second-order reaction