C6 - The Rate and Extent of Chemical Change

• Rate of a reaction - how fast the reactions are changed into products
• On a graph, a steeper line which plateaus sooner has a faster rate
• Rate of reaction depends on:

  • Collision frequency
  • Amount of energy transferred during each collision
• Activation energy - minimal amount of energy needed for particles to break bonds and react
• Rate of reaction depends on:

  • Temperature
  • Concentration of a solution / pressure of a gas
  • Surface area of reactants
  • Presence of a catalyst
• Increasing temperature increases rate:

  • Particles move faster
  • More frequent collisions
  • More energy of particles for collisions
• Increasing concentration / pressure:

  • More particles in the same area
  • More frequent collisions
• Increasing surface area of reactants increases rate:

  • Smaller pieces of solid means higher surface area to volume ratio
  • More opportunity for particles to collide so collisions happen more frequently
• Catalysts increase rate:

  • Lower activation energy
• Measuring rate of reaction:

  • Precipitation and colour change - timing how long it takes for a mark to disappear
  • Change in mass - measure before and after
  • Volume of gas released - gas syringe
• HCl reacts with:

  • Magnesium - forming H2 gas
  • Sodiym thiosulfate - cloudy precipitate
• Mean reaction rate = total mass change / total time
• Finding reaction rate on a graph for a point - find gradient of tangent
• Reversible reactions in equilibrium - forward and backward reactions happen at the same rate
• Equilibrium- both reactions still happen but there is no change in concentration of reactions and products
• Position of of equilibrium:

  • On the right - concentration of products is greater than reactants
  • On the left - concentration of reactants is greater than products
• Reversible reactions can be endothermic and exothermic:

  • If one direction is exo, the other is endo
  • Energy transferred to and from reaction is equal
• Le Chatelier's principle - if conditions of an equilibrium change, the equilibrium opposes the change
• Temperature increase - equilibrium shifts to endothermic direction
• Pressure increase - equilibrium shifts to direction with fewer moles of gas
• Concentration of products/reactants increase - equilibrium shifts to direction producing more of the other (products/reactants)