Rate and Extent of Chemical Change

• What is the term for how quickly a reaction happens?

  Rate of reaction
• How is the rate of reaction defined?

  Change in quantity divided by time
• What can the quantity in a rate of reaction refer to?

  Mass or volume of reactants or products
• What does the mean rate of reaction indicate?

  It averages the rate over the measurement period
• Describe an experiment to measure the rate of reaction using hydrochloric acid and sodium thiosulfate.

  • Use a conical flask over a marked paper cross
  • Observe when the solution turns cloudy
  • Stop timing when the cross is no longer visible
  • Repeat at different temperatures
• What does increased turbidity indicate in the reaction?

  The solution is becoming cloudy
• What is another method to measure the rate of reaction?

  Measuring the volume of gas produced
• What does a graph of gas volume against time typically look like?

  A curve that starts steep and levels out
• How do you find the rate of reaction at a specific time on a graph?

  Draw a tangent at that point
• What is the formula to calculate the rate of reaction using a tangent?

  Change in quantity divided by change in time
• What factors can increase the rate of a reaction?

  • Increasing concentration of reactants
  • Increasing pressure of gas reactants
  • Increasing surface area of solid reactants
  • Increasing temperature
  • Adding a catalyst
• Why does increasing temperature increase the rate of reaction?

  Particles move faster and collide more energetically
• What is the role of a catalyst in a reaction?

  It reduces the activation energy needed
• What happens to a catalyst during a reaction?

  It is not used up and remains unchanged
• What are reversible reactions?

  • Products can revert to reactants
  • Example: Haber process (ammonia production)
  • Both forward and reverse reactions occur
• What occurs in a closed system regarding reversible reactions?

  Both reactions reach a point of equilibrium
• What does it mean when the rates of forward and reverse reactions are equal?

  No overall change in quantities occurs
• What does Le Chatelier's principle state?

  Systems adjust to counteract changes in equilibrium
• How does increasing pressure affect a reaction with more moles on the left side?

  It favors the forward reaction
• What happens when the concentration of reactants is decreased?

  The position of equilibrium shifts towards the reactants
• How does temperature affect endothermic and exothermic reactions?

  Higher temperature favors endothermic reactions
• What is the relationship between forward and reverse reactions in reversible reactions?

  If one is exothermic, the other is endothermic
• What happens to the equilibrium when conditions change?

  The system adjusts to restore equilibrium