Energy and Enthalpy

• Lattice Enthalpy is the Enthalpy change due to the formation of one mole of ionic lattice from gaseous ions, an dso provides a measure of ionic bond strength. Lattice Enthalpy is always exothermic as it is bond formation.
• Standard Enthalpy change of formation is the Enthalpy change due to one mole of a compound forming from its constituent elements under standard conditions. This is always exothermic.
• Standard Enthalpy change of atomisation is the Enthalpy change by forming one mole of gaseous atoms from the element in its standard state under standard conditions. Enthalpy change of atomisation is always endothermic.
• If the element is a gas under standard conditions, then the Enthalpy change of atomisation would be based on bond Enthalpy.
• First electron affinity is the Enthalpy change when an electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous -1 ions. First electron affinity is exothermic, whilst successive ones are endothermic.
• Successive Electron affinities are endothermic, as adding an electron to an already negative ion requires the input of energy.
• First ionisation energy is the Enthalpy change required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions. This process is always endothermic as energy is needed to overcome the nuclear pull.
• Born-haber cycles can be used to determine Enthalpy changes concerning ionic lattices.
• The greater the ionic charge, the more exothermic the lattice Enthalpy, as there is a stronger attraction between ions.
• The smaller the ionic radius, the more exothermic the lattice Enthalpy as the stronger the attraction between ions.
• The Enthalpy change of hydration is the Enthalpy change when one mole of gaseous ions completely dissolves in water. The Enthalpy change of hydration is always exothermic.
• The Enthalpy change of solution is the Enthalpy change when one mole of a substance completely dissolves in water, and this can be exothermic OR endothermic.
• If the sum of enthalpies of hydration are greater than the lattice Enthalpy, then the Enthalpy of solution would be exothermic.
• If the sums of enthalpies of hydration are less than the lattice Enthalpy, then the Enthalpy of solution would be endothermic.
• Ionic charge and ionic radius effect the hydration Enthalpy and lattice Enthalpy.
• The smaller the ionic radius, the greater the attraction between the ions or water molecules, and so the more exothermic the lattice and hydration enthalpies.
• The greater the ionic charge, the greater the attraction between ions and water molecules, and so the more exothermic the lattice and hydration enthalpies.