The Rate and Extent of Chemical Change

• What is the formula for calculating the mean rate of reaction?

  mean rate of reaction = amount of reactant used or product formed / time taken
• How can the rate of reaction be measured?

  By measuring reactants used or products formed
• What should you measure if a product is a gas?

  Measure the mass before and after the reaction
• What happens to the mass of the reaction mixture when a gas is produced?

  The mass of the mixture will decrease
• What are the units for the rate of reaction when measuring mass?

  g/s
• How is the concentration of a reactant calculated?

  Concentration = amount (mol) / volume (dm³)
• What is the unit for concentration?

  mol/dm³
• How can you measure the volume of gas produced in a reaction?

  Using a gas syringe
• What is the unit for the rate of reaction when measuring gas volume?

  cm³/s
• How do you measure the time for a solution to change color?

  Time how long it takes to change color
• What are the four factors that affect the rate of reaction?

  • Temperature
  • Concentration
  • Surface area
  • Catalysts
• What happens to the rate of reaction at higher concentrations?

  The rate of reaction increases due to more collisions
• How does temperature affect the rate of reaction?

  Higher temperature increases particle movement and collisions
• How does increasing pressure affect the rate of reaction for gases?

  It increases the frequency of collisions
• What is the method to investigate how concentration affects reaction rates?

  1. Set up equipment
  2. Add hydrochloric acid and swirl
  3. Start timer
  4. Watch the cross through the flask
  5. Stop timer when cross disappears
  6. Repeat with different acid concentrations
• What is the independent variable in the concentration reaction experiment?

  The concentration of the acid
• What is the dependent variable in the concentration reaction experiment?

  The time for the cross to disappear
• What are the control variables in the concentration reaction experiment?

  Volume of acid and sodium thiosulfate
• What is the relationship between acid concentration and reaction time?

  Higher concentration leads to shorter reaction time
• What safety precautions should be taken during the experiment?

  Use eye protection due to corrosive acid
• Why do smaller pieces of solid reactants increase reaction rates?

  They have a larger surface area for collisions
• What are the key points to remember when plotting reaction rates on graphs?

  • Steeper line indicates faster reaction
  • Line becomes horizontal when reactants are used up
  • Same amount of product from same reactants
• How is the rate of reaction determined from a graph?

  By finding the gradient of the tangent
• What is a catalyst?

  A substance that increases reaction rate without being used up
• How do catalysts affect successful collisions?

  They reduce energy needed for successful collisions
• What role do enzymes play in biological systems?

  Enzymes act as catalysts
• Why is increasing reaction rates important in industry?

  It helps to reduce costs
• What are reversible reactions?

  • Reactions that can go forwards or backwards
  • Products can react to form original reactants
  • Represented as A(g) + B(g) ⇌ C(g) + D(g)
• What happens in an exothermic reaction in reverse?

  It becomes endothermic
• What is achieved in a closed system during a reversible reaction?

  An equilibrium is established
• What does Le Chatelier's Principle state?

  • System shifts to resist changes in conditions
  • In exothermic reactions, higher temperature decreases yield
  • In endothermic reactions, higher temperature increases yield
• How does pressure affect reactions involving gases?

  Higher pressure favors reactions with fewer gas molecules
• What happens if the concentration of a reactant is increased?

  The equilibrium shifts to form more products
• What occurs if the concentration of a reactant is decreased?

  The equilibrium shifts to form more reactants
• What factors determine optimum conditions in industrial processes?

  • Reaction rates
  • Concentration changes
  • Temperature adjustments
  • Pressure variations