Factors Affecting Lattice Enthalpy And Hydration Flashcards
What are the 3 general properties of ionic compounds?
- High melting and boiling points.
- Soluble in polar solvents.
- Conduct electricity when molten or in aqueous solution.
What two factors affect lattice enthalpy?
- Effect of ionic size.
- Effect of ionic charge.
What happens to the melting point of the lattice as ionic size/radius increases? Why?
The attraction between ions decreases and so the lattice energy becomes less negative and the melting point decreases.
What happens to the melting point of the lattice as ionic size/radius decreases? Why?
The attraction between the ions increases and so the lattice energy becomes more negative and the melting point increases.
What happens to the melting points of a lattice enthalpy as the ionic charge increases? Why?
As ionic charge increases, the attraction between the ions increases and so the lattice energy becomes more negative. This increases the melting point.
What happens to the melting points of the lattice enthalpy as the ionic charge decreases? Why?
As ionic charge decreases, the attraction between the ions decreases and so the lattice energy becomes less negative. This decreases the melting point.
What other factors can predict the size of the melting point other than the lattice enthalpy?
Factors like the packing of ions in an ionic lattice may need to be considered as well.
What two factors affect hydration enthalpies?
- Ionic size.
- Ionic charge.
What happens to hydration enthalpies as the ionic radius increases? Why?
The attraction between the ions and water molecules decrease and so hydration energy is less negative.
What happens to the hydration enthalpies as the ionic radius decreases?
The attraction between the ions and water molecules increases and so hydration energy is more negative.
What happens to the hydration enthalpies as the ionic charge increases? Why?
As the ionic charge increases, the attraction with the water molecules increases and so the hydration energy becomes more negative.
What happens to the hydration enthalpies as the ionic charge decreases? Why?
As the ionic charge decreases, the attraction with the water molecules decreases and so the hydration energy becomes less negative.
How can an ionic compound dissolved in water?
The attraction between the ions in the lattice must be overcome and 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.
How is it calculated the an ionic compound will dissolve in water?
If the sum of the hydration enthalpies is larger than the magnitude of the lattice enthalpy, the overall enthalpy change will be exothermic and the compound should dissolve.
What is a limitation regarding this calculation for solubility?
Many compounds with endothermic enthalpy changes of solution are soluble too.
