5.5 Standard Enthalpies of Formation

• Standard enthalpy of formation of a compound is the change in enthalpy that occurs when 1 mol of a compound is formed from its elements in their standard states
  • Standard State: a substance in its most stable state at SATP (25°C, 100 kPa) – state on the periodic table
  • Standard enthalpies of formation for Al2O3(s) is -1675.5 kJ/mol
  • Standard Enthalpy of formation for aluminum chloride is -704.2 kJ/mol

Example

Four Ways to Calculate Enthalpy Change

• Experimentally
  • measuring the heat of the surroundings (q)
  • hess’ law
• Theoretically
  • bond energies
  • standard enthalpies of formation