1.18 Enthalpies of Formation (1) S.J.T.U. Phase Transformation and Applications The enthalpy change of a material between states 1 and 2: △H=H2-H1 We could consider the mass itself to be a form of energy. Standard state A reference state:to assign a value of zero to enthalpy for certain materials in that reference state. Elements in their equilibrium states at 298 K and one atmosphere pressure. EX., Enthalpy of diatomic oxygen at 298 K and one atm:ZERO Enthalpy of monatomic oxygen at 298 K and one atm:NOT ZERO Enthalpy of graphite at 298 K and one atm:ZERO Enthalpy of diamond at 298 K and one atm:NOT ZERO SJTU Thermodynamics of Materials Spring2006©X.J.Jin Lecture 3 Second law IPhase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Spring 2006 © X. J. Jin Lecture 3 Second law I 1.18 Enthalpies of Formation (1) The enthalpy change of a material between states 1 and 2: Δ = − HHH 12 We could consider the mass itself to be a form of energy. A reference state: to assign a value of zero to enthalpy for certain materials in that reference state. Elements in their equilibrium states at 298 K and one atmosphere pressure. Ex., Enthalpy of diatomic oxygen at 298 K and one atm: ZERO Enthalpy of monatomic oxygen at 298 K and one atm: NOT ZERO Enthalpy of graphite at 298 K and one atm: ZERO Enthalpy of diamond at 298 K and one atm: NOT ZERO Standard state