rate and extent of chemical change

• what does a steeper line show in a rate of reaction graph?

  a faster rate of reaction
• what does a flat line show in a rates of reaction graph?

  reaction has finished
• what is the equation for mean rate of reaction?

  mean rate of reaction = amount of product formed or reactant used / time
• what are 3 common units of rate?

  • g/s
  • cm3/s
  • mol/s
• how do you find the rate on a rate of reaction graph?

  figure out the gradient using the equation:

  gradient = change in y / change in x
• how do you work out the mean rate over a period of time?

  mean rate = overall change in y / total time taken (change in x)
• what is the minimum energy particles require to react?

  activation energy
• what the rate of a chemical reaction depend on?

  • collision energy - more collisions between particles, faster rate of reaction. so doubling frequency of collisions would double the rate
  • collision frequency - enough energy needs to be transferred in a collision to overcome the activation energy and break the bonds to start the reaction.
• what will hot / cold temperatures do to the rate of reaction?

  • hot = fast
  • cold = slow
• what will low / high pressure do to the rate of reaction?

  • low = slow
  • high = fast
• what will big / small pieces do to the rate of reaction?

  • big = slow
  • small = fast
• what are catalysts?

  speed up reactions without being used up by providing an alternative pathway for the reaction
• is activation energy higher or lower with a catalyst?

  lower
• what are reversible reactions?

  where the products can react to form the reactants again
• when can equilibrium be reached?

  when a reversible reaction takes place in a closed system
• if there is more reactants in a reversible reaction, what side does the equilibrium lie on?

  left
• if a reversible reaction was exothermic one way, what would it be the other way?

  endothermic
• what happens if the temperature increases / decreases at equilibrium?

  • increases = equilibrium shifts to favour endothermic direction to take in heat energy
  • decreases = equilibrium shifts to favour exothermic direction to release heat energy
• what happens is the pressure increases / decreases at equilibrium?

  • increases = equilibrium shifts to favour the side with fewer molecules of gas to reduce the pressure
  • decreases = equilibrium shifts to favour the side with more molecules of gas to increase the pressure
• what is le chateliers principle?

  if the conditions of a reversible reaction at equilibrium are changed, the system tries to counteract the change
• if the concentration of reactants increases, system will?

  make more products
• if the concentration of reactants decreases, the system will?

  make more reactants