Definitions

• The standard enthalpy of atomisation is the enthalpy change when one mole of gaseous atom is formed from an element in its standard state
• Electron affinity is the standard enthalpy change when one mole of gaseous atom is converted into a mole of gaseous ions with a negative charge under standard conditions
• Ionisation energy is the standard enthalpy change used to remove one mole of an electron of one mole of an atom in its gaseous state to form a positive ion
• The standard enthalpy of formation is the enthalpy change where one mole of a substance is formed from its constituent elements under standard state and conditions
• The lattice of formation is the standard enthalpy change when one mole of solid ionic compound is formed from its gaseous ions. Example : Na+ (g) + Cl- (g) -> NaCl (s)
• The lattice dissociation enthalpy is the standard enthalpy change when one mole of solid ionic compound dissociates into its gaseous ions

  Example : NaCl (s) --> Na+ (g) + Cl- (g)
• Standard enthalpy changes are always measured at 298K, 100kPa and all substances are in their standard states.
• Enthalpy of combustion is the enthalpy change when one mole of a substance is burned completely in oxygen to produce carbon dioxide and water vapour
• Mean bond enthalpy is the energy required to break a covalent bond in 1 mole of gaseous compound to form two free radicals (averaged over a range compound )
• Enthalpy of hydration is the energy required to convert 1 mole of gaseous ions into aqueous ions
• Enthalpy of solution is the enthalpy change required to dissolve 1 mole of solute in enough solvent so that the aqueous ions are far enough apart to not interact
• Enthalpy of hydration is always exothermic because water molecules are polar so they attracted to ions this release energy
• Factors that affect enthalpy of hydration

  • The size of ions, the smaller the ion the larger the enthalpy of hydration
  • The larger the charge, the larger the enthalpy of hydration
• Entropy is the measure of disorder (S) so ∆S is the change in enthalpy. More disorder would increase entropy.

  Anything that changes state would affect the entropy

  
• Gibb's free energy is the measure of feasibility of a chemical reaction so 0 is greater than or equal to ∆G