Investigating Reaction Rates

• How can the rate of a reaction be measure?

  Measure the change in mass, measure the volume of gas produced (upside-down measuring cylinder or gas syringe), observe colour change / precipitate formed.
• When can the change in mass be used to measure the rate of reaction?

  When a gas is produced, gaseous molecules will be lost from the reaction vessel so fewer atoms in the reaction mixture, mass will decrease.
• Rate of reaction =

  Amount of product formed of reactant used / time
• Marble chips are added to HCl, how can the rate of reaction be measured?

  Measure the volume of gas produced and record the time.
• Why must you be careful when measuring the volume of gas produced with a gas syringe?

  You must ensure the volume produced will fit within the syringe otherwise it could damage the equipment and cause harm to the user.
• Why must the bung be immediately attached to the reaction vessel when measuring volume of gas produced?

  To ensure minimal gas escapes
• Name 3 ways the rate of reaction between HCl and marble chips could be increased

  Increased surface area of marble chips, increased concentration of acid, increased temperature of reactants
• Dilute HCl is added to sodium thiosulfate, how can the rate of reaction be measured?

  Place a 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 to disappear
• Why is the precipitate and colour change 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 determine the rare of a reaction at a particular time?

  Plot results on a graph, draw a tangent to the curve at this time, calculate the gradient (change in y / over change in x)
• Write a word equation or the rection between HCl and marble chips

  Hydrochloric acid + calcium carbonate -> water + calcium chloride + carbon dioxide
• How do you know that a reaction is complete?

  Mass of reaction mixture / volume of gas / colour remain the same
• How does temperature affect the rate of reaction?

  Increasing temperature increases the rate because particles have more kinetic energy so move faster (more frequent collisions) and more particles have energy above the activation energy (more collisions are successful).
• How does concentration of reactants affect the rate of a reaction?

  Increasing concentration increases the rate because there are more particles in the same volume so there are more frequent successful collisions.
• How does the pressure of the reactants affect the rate of a reaction?

  Increasing pressure increases the rate because there are more particles in the same volume (or the same number of particles in a smaller volume) so there are more frequent successful collisions.