22.3 - factors affecting lattice enthalpy and hydration

Created by

Gabriella Piper

Cards (10)

General properties of ionic compounds 
- High melting and boiling points.
- Soluble in polar solvents.
- Conduct electricity when molten or in aqueous solution.
Factors affecting lattice enthalpy 
Ionic size and ionic charge.
How does ionic size affect lattice enthalpy? 
- Ionic radius increases.
- Attraction between ions decreases.
- Lattice energy less negative (less exothermic).
- Melting point decreases.
How does ionic charge affect lattice enthalpy? 
- Ionic charge increases.
- Attraction between ions increases.
- Lattice energy becomes more negative (more exothermic)
-Melting point increases.
How can we predict melting points of ionic compounds from lattice enthalpy? 
The more negative (exothermic) a lattice enthalpy is the higher the melting point.
Factors affecting hydration 
Ionic size and ionic charge.
How does ionic size affect hydration? 
- Ionic radius increases.
- Attraction between ion and water molecules decreases.
- Hydration energy less negative (less exothermic).
How does ionic charge affect hydration? 
- Ionic charge increases.
- Attraction between ion and water molecules increases.
- Hydration energy becomes more negative (more exothermic).
What needs to be overcome to dissolve an ionic compound in water? 
Attraction between the ions in the ionic lattice. This requires a quantity of energy equal to the lattice enthalpy. Water molecules are attracted to the positive and negative ions, surrounding them and releasing energy equal to hydration enthalpy.
What must the sum of hydration enthalpies be in order for an ionic compound to dissolve? 
Sum of hydration enthalpies must be larger than the magnitude of the lattice enthalpy, the overall enthalpy change (of solution) will be exothermic and the compound should dissolve.