Rate of reaction

• What are the different speeds at which chemical reactions can take place?

  Very fast, moderately fast, and slow
• What are examples of very fast, moderately fast, and slow chemical reactions?

  • Very fast: Explosion of petrol-air mixture
  • Moderately fast: Reaction of reactive metals with acids
  • Slow: Rusting
• How can the rate of reaction be calculated?


  By measuring the amount of reactant used up, volume of gas produced, amount of product formed, or change in amount of reactant or product over time
• What quantities should be measured at regular time intervals to calculate the rate of reaction?


  The volume of gas produced and the change in mass
• What is the objective of the lesson on the rate of reaction?


  To interpret data obtained from experiments and suggest suitable methods to investigate the rate of reaction
• How can the speed of the reaction between dilute hydrochloric acid and calcium carbonate be determined?


  By collecting and measuring the volume of carbon dioxide produced at regular time intervals
• What is the procedure to study the rate of reaction between hydrochloric acid and calcium carbonate?


  1. Set up the apparatus.
  2. Add marble chips to hydrochloric acid and start the stopwatch.
  3. Shake the flask for complete reaction.
  4. Record the volume of carbon dioxide every 30 seconds.
  5. Plot a graph of volume against time.
• How is the rate of reaction determined from the graph of carbon dioxide volume against time?


  By drawing a tangent at a specific time and finding the gradient
• What does the shape of the graph indicate about the rate of reaction over time?


  It shows whether the rate of reaction changes or remains the same
• What does a steeper gradient on the graph indicate about the rate of reaction?


  A steeper gradient indicates a faster rate of reaction
• What happens to the gradient of the graph as the reaction proceeds?


  The gradient decreases, indicating that the rate of reaction is decreasing
• What is the chemical equation for the reaction between hydrochloric acid and calcium carbonate?


  2HCl (aq) + CaCO3 (s) → CaCl2 (aq) + H2O (l) + CO2 (g)
• What are effective collisions in a chemical reaction?


  Collisions between reacting particles that result in the formation of products
• What is activation energy (Ea)?


  The minimum amount of energy that reactant particles must possess for a chemical reaction to occur
• What factors affect the rate of reaction?


  1. Concentration of the reactants
  2. Pressure of the reactants (if gaseous)
  3. Particle size or surface area of the reactants
  4. Temperature of the reaction
  5. Presence of a catalyst
• How does concentration affect the rate of reaction?


  Higher concentration increases the rate of reaction due to more frequent collisions
• How does pressure affect the rate of reaction for gaseous reactants?


  Higher pressure increases the rate of reaction by bringing gaseous particles closer together
• How does particle size affect the rate of reaction?


  Smaller particle size increases the rate of reaction due to a larger surface area for collisions
• How does temperature affect the rate of reaction?


  Higher temperature increases the rate of reaction by increasing the energy and movement of particles
• What is the role of a catalyst in a chemical reaction?


  A catalyst increases the speed of reaction by lowering the activation energy
• What happens to the frequency of effective collisions when the concentration, pressure, particle size, and temperature increase?


  • Concentration: Increases frequency of collisions
  • Pressure: Increases frequency of collisions (gases)
  • Particle Size: Smaller size increases surface area for collisions
  • Temperature: Increases energy and movement of particles, leading to more collisions