5.6 Enthalpy Change Of Solution

Question 1

What is hydration enthalpy?

Answer 1

Enthalpy change when 1 mole of gaseous ions are surrounded by water molecules to form an infinitely dilute solution. Exothermic.

Question 2

What is enthalpy change of solution?

Answer 2

Enthalpy change when one mole of solute is dissolved in excess solvent to form a solution of infinite dilution. Endothermic or exothermic.

Question 3

What is lattice enthalpy a result of?

Answer 3

The electrostatic attractions between oppositely charged ions in the giant lattice.

Question 4

What does lattice enthalpy depend on?

Answer 4

Charge - the higher the charge on the ions the more strongly they will attract each other and therefore the greater the lattice enthalpy 2+2- > 2+1- > 1+1-
Size - the smaller the ions the stronger the attraction between them and therefore the larger the lattice enthalpy.
The effect of the charge on the ions is much larger effect than size variations.

Question 5

What do hydration enthalpies depend on?

Answer 5

The higher the charge the more exothermic the enthalpy change of hydration, the smaller the ions radius the more exothermic the enthalpy change of hydration. Higher charge and smaller size result in stronger attraction between the ions and water molecules. Again charge is more important.