Energy changes

• Exothermic reactions transfer energy to the surroundings which increases temperature. The products have less energy due to the transfer
• Endothermic reactions takes in energy from the surroundings which decreases temperature. The products have more energy due to the transfer
• in both exothermic and endothermic reactions, the energy rises to a peak which is the activation energy
• the activation energy is he minimum amount of energy required to react
• Bond calculations is the amount of energy needed to break the bond
• in bond calculations, the endothermic reactions are positive whereas the exothermic reactions are negative
• Temperature change required practical

  1. use measuring cylinder to measure 30$cm^3$of dilute HCL
  2. Transfer to a polystyrene cup in a beaker
  3. use thermometer to measure temperature of acid
  4. Measure $5cm^3$of sodium hydroxide and transfer to cup
  5. Place lid on top with hole and insert thermometer and stir. Record highest temperature reached
  6. Rinse cup and repeat experiment up to 40$cm^3$of sodium hydroxide in 5$cm^3$intervals
  7. Repeat whole experiment to calculate a mean
• a cell is two different metals in a electrolyte which produces electricity due to the reaction
• cells can only products electricity for a period of time until the chemicals run out
• cells only produce electricity if the metals have a different reactivity. the higher the difference in reactivity, the higher the voltage
• a battery is two or more cells in series
• rechargeable cells can be recharged using an electric current whereas in alkaline batteries, the reactants run out
• in a fuel cell, a fuel such as hydrogen is reacted with oxygen and water is the waste product
• half equation at the negative electrode in a fuel cell


  2H2 -> 4H+ + 4e-
• half equation at the positive electrode in a fuel cell


  02 + 4H+ + 4e- -> 2H2O
• overall equation in a fuel cell

  2H2 + O2 -> 2H2O
• positives of fuel cells 


  • produces electricity as long as you provide it
  • do not get less efficient
  • can be a source of drinking water
• negatives of fuel cells


  • Hydrogen is explosive so dangerous to store
  • produces a low voltage so several are needed together
• evaluation of rechargeable batteries

  • will run out and needs to be recharged
  • will store less electricity with each charging cycle so it will need to be replaced
  • produce a greater voltage than fuel cells