4. EEE-Lattice Enthalpy Flashcards
Lattice enthalpy
The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions
Always -ve
Indicates the strength of an ionic lattice
- enthalpy change of formation
The enthalpy change which occurs when one mole of a compound is formed from its constituent elements in their standard states under standard conditions
Usually -ve
- enthalpy change of atomisation
The enthalpy change which occurs when one mole of gaseous atoms is formed from the element in its standard state
Always +ve because bonds are broken
- first ionisation energy
The e c w o w one electron is removed from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
- first electron affinity
The e c w o w one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions
Enthalpy change of solution
The e c w o w one mole of a compound is completely dissolved in water
Can be endo or exothermic
Enthalpy change of hydration
The e c w o w one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions
Always -ve: exothermic
Example question:
Describe the factors that affect the values of lattice enthalpies
Decrease in size (ionic radius)
Increase in ionic charge/ charge density
= more negative/exothermic L.E.
Spec point:
Explain the effect of ionic charge and ionic radius on the exothermic value of a lattice enthalpy and enthalpy change of hydration
As
- ionic radius decreases
- ionic charge increases
L.E. And enthalpy change of hydration become more negative/exothermic
**worked eg in text book:
Why is magnesium oxide a good material for making the lining of furnaces?
MgO has a very negative lattice enthalpy
So there is a strong attraction between its ions
Therefore high melting point
It will be stable inside the furnace at high temperatures
