Rate and extent of chemical change

• Equation for the mean rate of reaction

  Mean ROR = quantity of reactant used or product formed / time taken
• Avagadro’s constant

  6.022 * 10^23 atoms per mole (mol)
• Factors that affect the ROR

  Concentration or surface area of reactants, pressure, temperature and the use of catalysts
• Activation energy


  Minimum amount of energy needed for particles to react
• Enzymes act as ________ in biological systems.

  catalysts
• How do catalysts increase the rate of reaction?


  By providing a different pathway for the reaction that has a lower activation energy.
• If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction. The same amount of energy is transferred in each case.
• Hydrated copper sulphate (blue) ⇌ anhydrous copper sulphate (white) + water

  Forwards reaction: endothermic

  Backwards reaction: exothermic
• The direction of reversible reactions can be changed by changing

  the conditions, for example:

  Ammonium chloride ⇌ ammonia + hydrogen chloride

  Forwards reaction: heated

  Backwards reaction: cooled
• What is dynamic equilibrium? 


  The state reached when the forwards and backwards reactions of a reversible reaction occur at the same rate in a closed system
• State Le Chatelier’s Principle


  If dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change and reestablish an equilibrium