Topic 5 - Energy changes

• What is conserved in chemical reactions?

  Energy
• What happens to the energy of product molecules in an exothermic reaction?

  They have less energy than reactants
• What is an exothermic reaction?

  Transfers energy to the surroundings
• What everyday items utilize exothermic reactions?

  Self-heating cans and hand warmers
• What is an endothermic reaction?

  Takes in energy from the surroundings
• What is a common application of endothermic reactions?

  Sports injury packs
• How can you distinguish between exothermic and endothermic reactions?

  • Based on temperature change of surroundings
  • Exothermic: temperature increases
  • Endothermic: temperature decreases
• What is the activation energy?

  Minimum energy for particles to react
• What do reaction profiles show?

  Relative energies of reactants and products
• How do you identify a reaction as exothermic or endothermic using a reaction profile?

  By observing the energy change direction
• What happens during a chemical reaction regarding energy?

  Energy is supplied to break bonds
• What is the overall energy change in an exothermic reaction?

  Energy released is greater than energy needed
• What is the overall energy change in an endothermic reaction?

  Energy needed is greater than energy released
• What do cells contain that produces electricity?

  Chemicals that react
• What factors affect the voltage produced by a cell?

  Type of electrode and electrolyte
• What is a battery?

  Group of cells connected in series
• What happens to non-rechargeable cells after use?

  They need to be discarded
• How do rechargeable cells work?

  Chemical reactions are reversed by current
• What do fuel cells require to produce electricity?

  External fuel and oxygen or air
• What is the overall reaction in a hydrogen fuel cell?

  Oxidation of hydrogen to produce water
• What is a potential benefit of hydrogen fuel cells?

  Alternative to rechargeable cells and batteries
• What should students be able to evaluate regarding cells?

  Use of hydrogen fuel cells vs. rechargeable cells
• What are the key points about chemical cells and batteries?

  • Cells produce electricity through chemical reactions
  • Voltage depends on electrode and electrolyte
  • Batteries are multiple cells in series
  • Non-rechargeable cells are discarded after use
  • Rechargeable cells can be recharged
• What are the key points about fuel cells?

  • Fuel cells use external fuel and oxygen
  • Hydrogen fuel cells oxidize hydrogen to produce water
  • They offer alternatives to rechargeable batteries