Rates of reaction

• What are three ways of measuring the rate of a reaction?

  - Observe how quickly a precipitate forms - Measure the change in mass - Measure the volume of gas given off
• How do you calculate the rate of reaction?

  Amount of product formed or reactant

  Used

  --------------------

  Time
• How could the rate of reaction be measured if a precipitate is produced?

  - Place piece of paper with a black cross below the reaction vessel and observe this cross through the solution - Measure how long it takes for the cross disappear
• How can you measure the rate of reaction if the coloured reactants form a colourless solution?

  Time how long it takes for the reactants to turn colourless
• Why is the precipitate rate experiment not very reliable?

  It is very subjective - people might disagree over the exact point when the mark disappears or the solution changes colour
• How can you measure the rate of reaction when there is a change in mass?

  Carry out the experiment on a mass balance: - Measure initial mass - Combine reactants - Take measurements of the mass at regular intervals as the reactants react - Rate = change in mass ÷ time
• How can you measure the rate of reaction when a gas is given off?

  - Add reactants to a conical flask - Immediately attach a gas syringe to the conical flask with a bung to ensure minimal gas escapes - Take regular measurements of the volume of gas in the gas syringe - Rate = total volume of gas produced ÷ time
• How can you find the rate of reaction of a reaction after 30 seconds?

  Plot results on a graph - X axis: time - Y axis: amount of product formed or reactant used Draw a tangent at 30 seconds and calculate the gradient (change in y ÷ change in x) to calculate the rate of reaction
• What are the units of rate of reaction if you are measuring a change in mass?

  g/s
• What are the units of rate of reaction if you are measuring the volume of gas given off?

  cm3 /s
• How could you investigate how HCl concentration affects the rate of reaction when magnesium is added?

  Gas is produced so the volume of gas produced can be measured:

  - Place the HCl in a conical flask

  - Add the magnesium ribbon and quickly fit the bung and gas

  syringe

  - Record volume of gas collected every 10 seconds

  - Repeat with a different concentration of HCl

  - Compare the rates for each concentration
• How could you investigate how sodium thiosulfate concentration affects the rate of reaction when reacted with HCl?

  Precipitate produced so measure the time it takes to cover a cross

  - Add 30cm3 of sodium thiosulfate to a conical flask

  - Add 10 cm3

  dilute HCl

  - Measure the time it takes for the cross to disappear

  - Repeat three times for mean time

  - Repeat the experiment with different concentrations of sodium thiosulfate

  - Compare the times for each experiment