Rates

• If rate is proportional to the concentration of reactant squared, reaction is second order 

   
• Reaction is first order 

  If rate is proportional to concentration of reactant
• Zero order

  • rate is not affected by concentration of reactant at all
• 2nd order example

  • concentration of reactant doubled
  • rate x4
• 1st order example

  • concentration of reactant doubled
  • rate doubled
• 0 order example

  • concentration of reactant doubled
  • rate doesn't change
• rate equation includes constant (k), concentration of reactants and order as their powers
• 1st order reactions have constant half lifes
• 2nd order reactions don't have constant half lifes
• in rate concentration graphs

  • 0 order reactants give a horizontal line
  • 1st order reactants give a sloping line
  • 2nd order reactants give a curved line
• Change in initial concentration is compared to change in initial rate
• If initial rate doesn't change - zero order for that reactant
• If initial rate changes by the square of the initial concentration factor (e.g. concentration doubled but rate quadruples) then second order for that reactant
• in a 0 order reaction, half life decreases with decreasing concentration
• in 1st order reaction half life stays constant whilst concentration decreases
• in a 2nd order reaction, half life increases with decreasing concentration
• concentration time graph

  • 0 order = straight line
  • 1st order = curve
  • 2nd order = steeper curve
• 1st order means the rate is proportional to concentration to the power of 1
• 0 order means the rate is proportional to concentration to the power of 0
• 2nd order means the rate is proportional to concentration to the power of 2
• in the rate equation, the bigger the K, the faster the rate
• in the rate equation the K is constant, provided the temperature is kept constant
• overall order = sum of individual orders