5-15. energetics

• Lattice enthalpy is either described as:

  • The enthalpy change when one mole of solid ionic compound is separated into gaseous ions under standard conditions
  • The enthalpy change when one mole of solid ionic compound is formed from its gaseous ions under standard conditions
• The lattice enthalpy depends on:

  • The charges on the ions: The bigger the charges on the ions, the higher the lattice enthalpy
  • The radius of the ions: The smaller the size of the ions, the higher the lattice enthalpy 
• The enthalpy of hydration is affected by:

  • The size of the ion: the greater the size of the ion, the weaker the attraction between the ions and water molecules so is a less exothermic process 
  • The charge of the ion: the greater the charge of the ion, the stronger the attraction between the ions and the water molecules so is a more exothermic process
• Enthalpy of atomisation:

  • This is the enthalpy change that occurs when one mole of gaseous atoms is formed from the element in its standard state and so energy is needed to break the bonds between the atoms 
  • always endothermic