Measuring enthalpy changes

• The standard molar enthalpy change of formation = Is the enthalpy change when one mole of substance is formed from its constituent elements under standard conditions, all reactants and products being in their standard states.
• The standard molar enthalpy of combustion = Is the enthalpy change when one mole of substance is completely burnt in oxygen under standard conditions, all reactants and products being in their standard states
• Temperature is related to the average kinetic energy of the particles in a system.

  Heat is a measure of the total energy of all the particles present in a given amount of substance.
• q = mcΔT

  (q=heat)

  (m=mass or substance being heated)

  (c=heat capacity of the substance)

  (ΔT=temperature change )

  ΔH = q / mol

  (ΔH=enthalpy change)
• The flame calorimeter

  • Spiral chimney is made of copper
  • Flame is enclosed
  • Fuel burns in pure oxygen
• Allowing for heat loss:

  • Polystyrene cup to prevent it by insulation