Chem chapter 5

• Fuel cells


  Hydrogen + oxygen
• Fuel cell operation


  1. Oxygen from electrolysis of water

  2. Hydrogen oxidised at anode, loses electrons

  3. Hydrogen ions flow to cathode, causing electrical current

  4. Oxygen reduced at cathode, reacts with hydrogen to form water
• Overall reaction in fuel cell: 2H2 + O2 -> 2H2O
• Fuel cells


  • Produce large amounts of electricity
  • No pollution gases
  • Do not need to be replaced
• Fuel cells


  • Expensive
  • Take up a lot of space
• Rechargeable batteries


  Simple cells that generate a voltage from a metal ion displacement reaction
• Voltage in rechargeable batteries

  Greater the difference in reactivity of metals, the higher the voltage
• Rechargeable batteries


  • Can be used more than once, better for environment
  • Lighter than alkaline batteries
• Rechargeable batteries


  • Contain heavy metals that are hard to recycle
  • Lower voltage compared to alkaline batteries
• Measuring temperature change in exothermic reaction

  1. Measure volume of reactants

  2. Measure maximum temperature reached

  3. Repeat with increasing concentrations

  4. Plot graph of results
• Enthalpy change


  • Energy change: total bond energy of reactants - total bond energy of products
  • Negative value = exothermic, positive value = endothermic
• • Exothermic reactions release energy and warm the surroundings
  • Endothermic reactions absorb energy from the surroundings and cool them