Thermodynamics

• enthalpy of formation: enthalpy when one mole of a substance is formed from its constituent elements with all substances in their standard states
• enthalpy of formation = -ve or +ve

  2Na + 1/2 O2 --> Na2O
• enthalpy of combustion: enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all substances in standard states
• enthalpy of combustion = -ve

  H2 + 1/2 O2 --> H2O
• ionisation energy (first) : enthalpy change when each atom in one mole of gaseous atoms loses one electron to form one molecule of gaseous 1+ ions
• ionisation energy (first) = +ve

  Mg --> Mg+ + e-
• ionisation energy (second): enthalpy change when each ion in one mole of gaseous 1- ions gains one electron to form one mole of gaseous 2+ ions
• ionisation energy (second) = +ve

  Mg+ --> Mg2+ + e-
• electron affinity (first) : enthalpy change when each ion in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions
• electron affinity (first) = -ve

  O + e- --> O-
• electron affinity (second): enthalpy change when each ion in one mole of gaseous 1- ions gains one electron to form one mole of gaseous 2- ions
• electron affinity (second) = +ve

  O- + e- --> O2-
• bond dissociation: enthalpy change when one mole of covalent bonds is broken in the gaseous state
• bond dissociation = +ve

  I2 --> 2I
• enthalpy of atomisation of an element: enthalpy change when one mole of gaseous atoms is produced from an element in its standard state
• enthalpy of atomisation of an element = +ve

  I2 --> 2I
• enthalpy of atomisation of a compound: enthalpy change when gaseous atoms are produced from one mole of a compound in its standard state
• enthalpy of atomisation of a compound = +ve

  1/2 I2 --> I
• lattice enthalpy of formation: enthalpy change when gaseous atoms are produced fomr one mole of a compound in its standard state
• lattice enthalpy of formation = -ve

  Mg2+ + 2Cl- --> MgCl2
• lattice enthalpy of dissociation: enthalpy change when one mole of solid ionic compound is broken up into its constituent ions in the gas phase
• lattice enthalpy of dissociation = +ve

  MgCl2 --> Mg2+ + 2Cl-
• hydration enthalpy: enthalpy change when one mole of gaseous ions become hydrated
• hydration enthalpy = -ve

  Mg2+ (g) --> Mg2+ (aq)
• enthalpy of solution: enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well separated and do not interact with each other
• enthalpy of solution = -ve or +ve

  NaCl --> Na+ + Cl-