Endothermic and Exothermic Reactions

• What is conserved in chemical reactions?

  Energy
• What happens to the overall amount of energy in the universe after a reaction?

  It remains the same
• What characterizes an endothermic reaction?

  It takes in energy from surroundings
• What is shown by a fall in temperature?

  Endothermic reaction
• What are examples of endothermic reactions?

  • Thermal decomposition
  • Dissolving sodium hydrogencarbonate
  • Some sports injury packs
• What characterizes an exothermic reaction?

  It transfers energy to surroundings
• What is shown by a rise in temperature?

  Exothermic reaction
• What are examples of exothermic reactions?

  • Combustion
  • Most oxidation reactions
  • Self-heating cans and hand warmers
• What do reaction profiles illustrate for endothermic and exothermic reactions?

  • Endothermic: Energy absorbed, temperature falls
  • Exothermic: Energy released, temperature rises
• What is activation energy (Ea)?


  Minimum energy needed for reactants to react
• What is the relationship between bond breaking and energy changes?

  • Bond breaking: Endothermic (energy absorbed)
  • Bond forming: Exothermic (energy released)
• What happens to energy during bond breaking in endothermic reactions?

  Energy used exceeds energy released
• How is overall energy change calculated in reactions?

  Total energy needed minus total energy released
• How can bond energies be utilized in chemical reactions?

  • Calculate energy changes
  • Determine if reactions are endothermic or exothermic