• The?rate of reaction?refers to the change in the amount or concentration of a reactant?or?product per unit time
  • The units for rate of reaction are mol dm-3?s-1
• It can be found by measuring:
  • The?mass lost?over time
  • The?volume of produced?over time
  • Colour changes, including by the use of colorimetry
  • pH changes over time
  • Changes in electrical conductivity
• The rate of reaction can be calculated by:

Rate of reaction =

Rate of Reaction

• A?directly proportional?relationship between the?rate?of reaction and?concentration of D?is observed when the results are plotted on a graph:

Rate of reaction over various concentrations of D

• This leads to a very common rate expression:

Rate ∝ [D]? ? ? ?or? ? ? ?Rate =?k[D]

• This rate expression means that if the concentration of D is doubled, then the rate doubles
• Equally, if the concentration of D halves, then the rate halves

Rate Equations

• The following reaction will be used to discuss rate equations:

A (aq) + B (aq) → C (aq) + D (g)

• The rate equation for this reaction is:

Rate of reaction =?k?[A]m?[B]n

• Rate equations can?only?be determined?experimentally?and cannot be found from the?stoichiometric equations
• In the above rate equation:
  • [A] and [B] are the concentrations of the reactants
  • m?and?n?are orders with respect to each reactant involved in the reaction

   

• Products and catalysts may feature in rate equations
• Intermediates do not feature in rate equations