Rates of Reaction (C6)

• How is the rate of reaction defined?

  Change in quantity divided by time
• What is the term for how quickly a reaction happens?

  Rate of reaction
• What quantities can be measured to determine the rate of reaction?

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

  Average 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 cross
  • Observe cloudiness as the reaction occurs
  • Stop timing when the cross is no longer visible
  • Repeat at different temperatures
• What does increased turbidity indicate in the reaction?

  Formation of a cloudy solution
• What is a method to measure gas production in a reaction?

  Using a gas syringe
• What does a graph of gas volume against time typically look like?

  Starts steep, then levels out
• How can you find the rate of reaction at a specific time from 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 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
• Why does increasing temperature affect reaction rates?

  Particles move faster and collide more often
• What is activation energy?

  Minimum energy needed for a reaction
• What role does a catalyst play in a reaction?

  Reduces activation energy needed
• What happens to a catalyst during a reaction?

  It is not used up
• What are reversible reactions?

  • Products can revert to reactants
  • Example: Haber process for ammonia
  • Equilibrium reached in a closed system
• What occurs at equilibrium in a closed system?

  Rates of forward and reverse reactions equal
• What does Le Chatelier's principle state?

  System adjusts to counteract changes
• How does increasing pressure affect a reaction with more moles on the left side?

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

  Equilibrium shifts towards the side with fewer moles
• 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 forward is exothermic, reverse is endothermic
• What is an example of an endothermic reaction in reversible processes?

  Breaking down ammonia
• What happens to the reaction rates when conditions change?

  Rates of reactions will adjust accordingly
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