Rates of reaction

• What do catalysts do in chemical reactions?

  Change the rate without being used up
• Why do different reactions require different catalysts?

  Each reaction has unique activation energy needs
• What role do enzymes play in biological systems?

  Act as catalysts
• How do catalysts increase the rate of reaction?

  By providing a pathway with lower activation energy
• What does a reaction profile for a catalyzed reaction illustrate?

  • Activation energy without catalyst
  • Activation energy with catalyst
  • Progress of reaction
• How can students identify catalysts in reactions?

  By their effect on reaction rate
• What should students explain about catalytic action?

  It relates to activation energy
• What is the formula for mean rate of reaction?

  Quantity of reactant used / time taken
• How can the quantity of reactant or product be measured?

  By mass in grams or volume in cm³
• What are the units of rate of reaction?

  g/s or cm³/s
• What additional requirement is there for Higher Tier students regarding rates of reaction?

  Use quantity of reactants in moles
• How can students calculate the mean rate of a reaction?

  From reactant used or product formed
• What should students be able to draw and interpret regarding reactions?

  Graphs of product formed or reactant used
• How do students use tangents on reaction graphs?

  To measure the rate of reaction
• What factors affect the rate of chemical reactions?

  Concentration, pressure, surface area, temperature, catalysts
• What does collision theory explain?

  How factors affect rates of reactions
• What is activation energy?

  The minimum energy needed for a reaction
• How does increasing concentration affect reaction rates?

  Increases frequency of collisions
• What happens to reaction rates when temperature increases?

  Particles move faster, increasing collisions
• How does surface area affect reaction rates?

  More particles available for collisions
• How can students predict the effects of changing conditions on reaction rates?

  Using collision theory
• What is the relationship between surface area and volume ratio?

  Smaller pieces have a higher ratio
• What is the formula for calculating the rate of reaction?

  Amount of product / time taken
• What is a successful collision?

  A collision that leads to a reaction
• How does increasing temperature affect successful collisions?

  Increases the percentage of successful collisions
• What are the five factors affecting the rate of a reaction?

  • Concentration
  • Pressure
  • Surface area
  • Temperature
  • Presence of catalysts
• How does a catalyst affect activation energy?

  Reduces activation energy for reactions
• What is the effect of increasing surface area on reaction rates?

  Increases the rate of reaction
• What happens to the rate of reaction as reactants are used up?

  Rate decreases as fewer particles collide
• What is the initial rate of reaction?

  The rate at the start of the reaction
• How does the collision theory relate to reaction rates?

  Particles must collide with enough energy
• How can students calculate the rate of reaction from mass change?

  Change in mass / time taken
• How can students measure the rate of reaction using gas production?

  Using a gas syringe or measuring cylinder
• What is the purpose of measuring time in reaction experiments?

  To calculate the rate of reaction
• What is the effect of temperature on particle energy?

  Higher temperature increases particle energy
• How does the presence of a catalyst affect reaction pathways?

  Provides an alternative pathway with lower energy
• How does increasing temperature affect the frequency of collisions?

  Increases frequency and energy of collisions
• What is the relationship between activation energy and successful collisions?

  Higher activation energy means fewer successful collisions
• What is the role of temperature in collision theory?

  Increases particle movement and collision frequency
• How does increasing concentration affect the rate of reaction according to collision theory?

  More particles lead to more frequent collisions