lattice enthalpy

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  • lattice enthalpy
    • definition: energy change when one mole of an ionic compound is formed from its gaseous ions at 25 degrees and 1 atm
    • exothermic-always has negative value
    • standard enthalpy change of atomisation: enthalpy change when one mole of gaseous atoms are formed from the element in its standard state
    • 1st electron affinity: enthalpy change when one electron is added to each atom in one mole of gaseous atoms to form gaseous uni NEGATIVE ions
    • size and charge of ions affects LE
      • LE becomes less exothermic (more positive) as the SIZE of the ions increase
        • radius of ion increases so attraction between ions decreases
      • LE becomes more exothermic (more negative) as the charge on the ion increases
        • this means that ions will have a greater charge density so stronger ionic bonds
    • enthalpy change of solution: energy change when 1 mole of a ionic solid is totally dissolved in water
    • enthalpy change of hydration: energy change when one mole of gaseous ions totally dissolve in water
      • always exothermic (requires energy)
      • always larger (more exothermic) for ions that have small ionic radii and larger charges.
        • this increases chrge density of the ions and attraction between ions and water molecules is also increased
    • Hle=     Hhyd-  Hsol


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