13.1.3 - Enthalpy changes of solution and hydration

Question 1

Why do most ionic compounds dissolve in water?

Answer 1

The ionic lattice is broken down and the ions become surrounded with water molecules so ions are hydrated

Question 2

What is the enthalpy change of solution?

Answer 2

The enthalpy change when one mole of ionic solid dissolves in water to form an infinitely dilute solution.

Question 3

What is the enthalpy change of hydration?

Answer 3

The enthalpy change when one mole of an ion in its gaseous state is completely hydrated in water

Question 4

What is an infinitely dilute solution?

Answer 4

When a solution reaches a point where further dilution makes no difference.

Question 5

Write an equation for the enthalpy change of solution for sodium chloride.

Answer 5

NaCl (s) = Na+ (aq) + Cl- (aq)

Question 6

Write an equation for the enthalpy change of hydration for a sodium ion.

Answer 6

Na+ (g) = Na+ (aq)

Question 7

Are values for the enthalpy change of solution and hydration positive or negative or both?

Answer 7

Enthalpy change of solution = negative or Positive
Enthalpy change of hydration = always negative

Question 8

What is the name of the interaction between an ion and water when it’s being hydrated?

Answer 8

Ion - dipole interaction

Question 9

What happens to the value of enthalpy change of hydration when charge density increases?

Answer 9

It becomes more negative as there is a stronger attraction to water