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Question 1

What do most ionic substances dissolve in?

Answer 1

in polar solvents eg. Water

Question 2

What happens when an ionic solid dissolves in water?

Answer 2

Ion dipole bonds form between the water molecules and the dissolved ions
The ions separate from the ionic lattice and become surrounded by water molecules (hydration)
an aqueous solution is made

Question 3

What is lattice enthalpy?

Answer 3

The enthalpy change when 1 mole of an ionic lattice is formed from its gaseous ions under standard conditions

Question 4

Why is lattice enthalpy always negative?

Answer 4

Because bonds are always broken and energy is released

Question 5

What is an example of an equation for lattice enthalpy?

Answer 5

Na+ (g) + Cl- (g) -> NaCl(s)

Question 6

When do lattice enthalpies become more negative?

Answer 6

• When ionic charge increases
• When ionic radii decreases

Question 7

What happens when an ionic lattice dissolves into water?

Answer 7

1) bonds between the ions break (dissociation enthalpy)
2) bonds between the ions and the water are made (formation enthalpy)

Question 8

What is the value for lattice dissociation enthalpy?

Answer 8

Positive as the reaction is endothermic
AND
The opposite of lattice enthalpy

Question 9

What is lattice dissociation enthalpy?

Answer 9

The enthalpy change when one mole of a solid ionic compound is completely dissociated into its gaseous constituent ions under standard conditions

Question 10

What is lattice formation enthalpy?

Answer 10

The enthalpy change when one mole of a solid ionic compound is formed from its gaseous constituents under standard conditions

Question 11

What type of value is lattice formation enthalpy?

Answer 11

Negative as it is exothermic

Question 12

How is lattice enthalpy obtained?

Answer 12

Using the Bon-Hager cycle

Question 13

What is enthalpy of solution?

Answer 13

The enthalpy change when one mole of ionic solid is dissolved in water to infinite dilution under standard conditions

Question 14

What is enthalpy of hydration?

Answer 14

The enthalpy change when one mole of gaseous ions dissolves in water to form one mole of aqueous ions under standard conditions

Question 15

What is an example of an enthalpy of hydration equation?

Answer 15

Na+(g) -> Na+ (aq)

Question 16

What is an example of an enthalpy of solution equation?

Answer 16

NaCl(s) -> NaCl(aq)

Question 17

Why is enthalpy of hydration negative?

Answer 17

Because water molecules have positive regions that attract negative ions

Question 18

What is the equation for enthalpy change in solution?

Answer 18

Question 19

Answer 19

A) Lattice enthalpy
B) enthalpy of solution
C) Enthalpy of hydration for Cl- + Enthalpy of hydration for Na+

Question 20

What happens to hydration enthalpies as you move down a group?

Answer 20

Decreases as ions get larger

Question 21

Why does an Na+ ion have a lower Enthalpy of hydration than Mg2+?

Answer 21

Because it has a lower charge

Question 22

Enthalpy level diagram for a solute with a negative enthalpy of solution

Answer 22

Question 23

Enthalpy level diagram for a solute with a positive enthalpy of solution

Answer 23

Question 24

What happens if you try and dissolve an ionic substance in a NON-polar solvent?

Answer 24

• The solvent is unable to interact strongly with the ions
• So the lattice is not broken apart and lattice enthalpy is small
• so enthalpy of solution is large and positive
• Dissolved;vying is unlikely to occur