Controlling Chemical Reactions

• What is the purpose of determining the rate of a given reaction?


  To understand how different factors affect the speed of the reaction
• What factors can affect the rate of a chemical reaction?

  • Surface area/particle size
  • Concentration
  • Temperature
  • Use of a catalyst
• How can the rate of reaction be measured using the amount of product formed?


  Rate of reaction = amount of product formed / time
• How can the rate of reaction be calculated using the amount of reactant used?


  Rate of reaction = amount of reactant used / time
• What units can be used to express the rate of reaction?


  g/s or cm³/s
• How can the quantity of reactants or products be measured?


  By mass in grams or by volume in cm³
• Why would you conduct multiple experiments when changing a variable like temperature?


  To compare the rates of reaction at different temperatures
• How can the volume of gas produced in a reaction be measured?

  Using a gas syringe or an upside-down measuring cylinder
• What should be done with the total volume of gas collected during a reaction?


  Record it at regular intervals and plot a graph
• How do you find the rate of reaction when gas is produced?


  Rate of reaction = volume of gas / time taken
• What happens to the concentration of products as a reaction proceeds?


  It increases
• What happens to the concentration of reactants as a reaction proceeds?


  It decreases
• What does the gradient of the line on a rate of reaction graph represent?


  The rate of reaction
• How is 1/t related to the rate of reaction?


  1/t is proportional to the rate of reaction
• What effect does increasing temperature have on the rate of reaction?


  It increases the rate of reaction
• How does increasing concentration affect the rate of reaction?


  It increases the frequency of collisions
• What is the effect of increasing pressure on the rate of reaction for gases?


  It increases the frequency of collisions
• What does a greater surface area to volume ratio imply for the rate of reaction?


  It means a greater rate of reaction
• How does the surface area to volume ratio change with smaller pieces of solid?


  The ratio increases
• What is the role of catalysts in chemical reactions?


  Catalysts speed up reactions without being changed
• What are enzymes in the context of catalysts?


  Enzymes are biological catalysts
• How do catalysts affect activation energy?

  Catalysts provide an alternative pathway with lower activation energy
• What happens to the number of particles with energy greater than the activation energy when a catalyst is used?


  The number of such particles increases
• What is the role of enzymes in biological systems?


  Enzymes act as catalysts