Chapter 18 RATES OF REACTIONS

• What is the iodine clock reaction used to measure?

  Rate of reaction
• What assumption is made about the rate during the iodine clock experiment?

  The rate stays constant
• What must remain constant for the iodine clock reaction to occur?

  Temperature
• How can the rate of reaction be measured?

  By mass lost, gas given off, etc.
• What indicates that the endpoint of the reaction has been reached?

  The reaction has not proceeded too far
• What does the gradient of the tangent represent in a reaction rate graph?

  Rate of reaction
• What is the initial rate of a reaction?

  Rate at the start of the reaction
• What is the chemical equation for the iodine clock experiment?

  H2O2(aq) + 2I-(aq) + 2H+(aq) → 2H2O(l) + I2(aq)
• What is added to the excess H2O2 in the iodine clock experiment?

  Sodium thiosulphate and starch
• What happens when sodium thiosulphate is used up in the iodine clock experiment?

  Iodine reacts with starch, turning blue-black
• How does varying the concentration of iodine or H2O2 affect the experiment?

  Changes the time for color change to occur
• What is the relationship between concentration and rate of reaction?

  • Changes in concentration affect rate
  • Concentration changes have a squared proportional effect
• What can only be worked out from the orders of reaction?

  Rate equation and concentration effects
• What is the rate equation format?

  Rate = k[A][B]
• What does the rate constant depend on?

  Temperature
• What happens to the rate constant as temperature increases?

  It becomes larger
• What effect does a catalyst have on the rate of reaction?

  It speeds up the reaction
• What is the half-life in a reaction?

  Time taken for half of reactant to be used
• What should you always calculate in an experiment if needed?

  Rate constant k
• What does the Arrhenius equation link together?

  Activation energy and temperature to rate constant
• What happens to the activation energy as the rate constant increases?

  Activation energy gets smaller
• What happens to the rate constant as activation energy decreases?

  Rate constant gets bigger