C5

• What is the energy change in endothermic reactions?

  Energy needed to break bonds is greater
• What happens in exothermic reactions?

  Energy released is greater than energy taken
• What is the definition of an endothermic reaction?

  • Energy is taken in from surroundings
  • Surrounding temperature decreases
• What is the definition of an exothermic reaction?

  • Energy is transferred to surroundings
  • Surrounding temperature increases
• What is activation energy?

  Minimum energy for colliding particles to react
• What does a reaction profile diagram show?

  Overall energy changes in a reaction
• What must happen for a reaction to take place?

  Bonds in reactants must be broken first
• Why is bond breaking considered an endothermic process?

  It requires energy to break bonds
• Why is bond forming considered an exothermic process?

  It releases energy when new bonds form
• What is the energy change in a reaction profile diagram?

  • Difference between reactants and products
  • Indicates whether reaction is endothermic or exothermic
• What happens to the temperature of surroundings in an endothermic reaction?

  The temperature of surroundings decreases
• What happens to the temperature of surroundings in an exothermic reaction?

  The temperature of surroundings increases
• How is activation energy represented in a reaction profile diagram?

  Difference between reactants and the peak
• How do you calculate the energy change in a reaction?

  1. Use bond energies measured in kJ/mol
  2. Calculate energy needed to break bonds
  3. Calculate energy released in forming bonds
  4. Subtract bond making from bond breaking
• What is the overall energy change for the reaction N2 + 3H2 ⇌ 2NH3?

  -93 kJ/mol
• Why is the reaction N2 + 3H2 ⇌ 2NH3 considered exothermic?

  Overall energy change is negative