C5: energy changes

• Endothermic reaction


  Reaction that feels like it gets colder
• Exothermic reaction


  Reaction that feels like it gets hotter
• Endothermic reaction


  Reaction that takes energy in
• Exothermic reaction


  Reaction that gives energy out
• Endothermic reactions


  • Electrolysis
• Exothermic reactions


  • Burning
  • Neutralization
• Calculating energy change for a reaction

  1. Write balanced equation

  2. List bond types and numbers

  3. Multiply bond energies

  4. Calculate energy change
• Reactions with negative energy change are exothermic
• Cell


  Single unit that produces electricity
• Battery


  Multiple cells connected together
• Non-rechargeable batteries


  • Chemical reaction that produces electricity is used up
  • Battery is then dead
• Rechargeable batteries


  • Reversible chemical reaction
  • Can be recharged by passing electricity through
• Hydrogen fuel cell


  Hydrogen gas reacts with oxygen gas to produce water and release energy
• Hydrogen fuel cells


  • Large amount of energy released
  • Only product is water, no carbon emissions
  • Issues with hydrogen production and storage
• Hydrogen fuel cell reactions

  1. At negative electrode: Hydrogen gas - 2 electrons -> Hydrogen ions

  2. At positive electrode: Hydrogen ions + Oxygen gas + Electrons -> Water