C8: rates and equilibrium

• Rate of reaction


  The amount of product made in a certain amount of time OR the amount of reactant used up in a certain amount of time
• Calculating mean rate of reaction

  1. Know amount of product made or reactant used

  2. Know time taken

  3. Divide amount by time
• Measuring rate of reaction

  • For gases: use gas syringe to measure volume or balance to measure mass decrease
  • For non-gases: look for color change
• Rate of reaction is greatest at the start and slows down as reaction proceeds
• Calculating instantaneous rate of reaction

  1. Draw tangent to graph

  2. Calculate gradient of tangent
• Collision theory


  Reactions only occur if reactants have enough energy and collide in the correct orientation
• Factors affecting rate of reaction

  • Increasing temperature
  • Increasing concentration
  • Increasing surface area
• Catalyst


  Provides alternative reaction pathway with lower activation energy
• Advantages of catalysts


  • Do not get used up
  • Allow lower reaction temperatures
• Disadvantages of catalysts


  • Often expensive rare metals
  • Usually specific to one reaction
• Reversible reaction


  Reaction that can go in both forward and backward directions
• In a reversible reaction, forward reaction is endothermic, backward reaction is exothermic
• Dynamic equilibrium


  When forward and backward reactions occur at the same rate in a closed system
• Le Chatelier's principle


  A reversible reaction will counteract any change to shift the equilibrium
• Increase temperature


  Favors endothermic backward reaction
• Increase pressure


  Favors product with fewer moles
• Increase reactant concentration


  Shifts equilibrium to produce more product