RP 3: Effect of Temp on Rate of Reaction

• How can rates of reaction be measured?

  • Initial rate method (i.e. iodine clock).
  • Continuous rate monitoring (i.e. amount of gas released over time).
• Why does increasing temperature increase the rate of reaction?

  • Higher temperature = higher kinetic energy.
  • More molecules have energy greater than the activation energy so are able to react.
  • As KE increases, velocity of particles also increases, resulting in more frequent collisions.
• How would you investigate how the rate of this reaction increases with temperature? :

  Sodium thiosulphate + HCl

  • This reaction produces a cloudy sulphur precipitate.
  • To measure rate, time how long it takes a cross underneath the beaker to disappear using a stopwatch.
  • Repeat at 5+ temperatures and compare times taken.
• What are some issues with the cross method?

  • Judged by eye so can be reliable/subjective.
  • May be delayed time on stopwatch.
  • May be too slow at low temperatures.
  • May not be enough precipitate for the cross to disappear.
• When investigating the effect of Temp on r.o.r, what variables should be controlled?

  • Concentrations of reactants/products.
  • Volumes of reactants/products.
  • Same beaker/cross.
  • Same person to decide when cross disappears.
• How do you keep a substance at a constant temperature?

  Use a water bath.