Rate of reaction

• Rate of reaction


  • Amount of reactant used / Time
  • Amount of product formed / Time
• Calculating rates of reactions

  • Quantity of reactant or product can be measured by mass in grams or volume in cm3
  • Units of rate of reaction may be g/s or cm3/s
  • Can use quantity of reactants in moles and units for rate of reaction in mol/s
• Finding rate of reaction graphically

  1. Draw tangents to curves

  2. Use the slope of the tangent as a measure of rate of reaction at a specific time
• Factors which affect the rates of chemical reactions

  • Concentration
  • Pressure
  • Surface area
  • Temperature
  • Catalysts
• Collision theory


  Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy
• Activation energy


  The minimum amount of energy that particles must have to react
• Increasing concentration, pressure, surface area

  Increases the frequency of collisions and so increases the rate of reaction
• Increasing temperature


  Increases the frequency of collisions and makes the collisions more energetic, and so increases the rate of reaction
• Catalysts


  Substances that speed up chemical reactions without being changed or used up during the reaction
• Enzymes act as catalysts in biological systems
• Catalysts are not included in the equation for a reaction
• How catalysts work


  • Decrease the activation energy, increasing the proportion of particles with energy to react
  • Provide an alternate athway for a chemical reaction that has a lower activation energy