Measuring enthalpy changes

• Calculating an energy change

  q = mcΔT

  • m- mass of the surroundings measured in grams
  • c - specific heat capacity of the surroundings
  • Δt- the temperature change
• The specific heat capacity is the energy required to raise the temperature of one gram of a substance by 1 K.
• The specific heat capacity of water is 4.18.
• Reasons to get a different value of enthalpy change of combustion:

  • heat loss to the surroundings other than water- the beaker or air
  • incomplete combustion of fuel
  • evaporation of fuel from the wick
  • non-standard conditions
• Determination of an enthalpy change of combustion

  1. calculate the energy change of the water in kJ
  2. calculate the amount in mol of fuel burnt mass / Mr
  3. calculate the enthalpy change of combustion in kJ/mol
• Determination of an enthalpy change of a reaction for a solid and solution

  1. Calculate the energy change in the solution in kJ
  2. Calculate the amount, in mol, of solution that reacted with the excess solid
  3. calculate the enthalpy change of reaction in kJ/mol
• Determination of an enthalpy change of neutralisation

  1. calculate the energy change in the solution in kJ
  2. calculate the amount, in mol, of acid and base that reacted
  3. calculate the enthalpy change of reaction in kJ/mole