1.1 Lattice Enthalpy

Question 1

Define ionic bonds

Answer 1

Strong electrostatic forces of attraction between oppositely charged ions

Question 2

Define lattice enthalpy

Answer 2

the enthalpy change when one mole of an ionic compound is converted to gaseous ions

Question 3

Give an equation to express the lattice enthalpy of sodium chloride

Answer 3

NaCl(s) → Na+ (g) + Cl- (g)

Question 4

Describe the value of lattice enthalpy

Answer 4

• will be endothermic (+ve) as energy is required to break the ionic bonds
• a large value for lattice enthalpy shows there are strong electrostatic forces of attraction between the oppositely charged ions in the lattice.

Question 5

Define the standard enthalpy change of formation

Answer 5

The energy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.

Question 6

Give an equation to express the standard enthalpy change of formation of potassium chloride

Answer 6

K(s) + ½ Cl2(g) → KCl(s)

Question 7

Define standard enthalpy change of atomisation

Answer 7

The enthalpy change when one mole of gaseous atoms is formed from the element in its standard state

Question 8

Give an equation to express the standard enthalpy change of atomisation of potassium

Answer 8

K(s) → K(g)

Question 9

Give an equation to express the standard enthalpy change of atomisation of chlorine

Answer 9

½ Cl2(g) → Cl(g)

Question 10

Define the standard bond dissociation enthalpy

Answer 10

The enthalpy change required to break 1 mol of a covalent bond, everything being in the gas state.

Question 11

Give an equation to express the standard bond dissociation enthalpy of chlorine

Answer 11

Cl2(g) → 2Cl(g)

Question 12

Define first ionisation energy

Answer 12

The enthalpy change accompanying the removal of one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Question 13

Give an equation to express the first ionisation energy of potassium

Answer 13

K(g) → K+(g) + e-

Question 14

define second ionisation energy

Answer 14

The enthalpy change accompanying the removal of one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.

Question 15

give an equation to express the second ionisation energy of calcium

Answer 15

Ca+(g) → Ca2+(g) + e-

Question 16

Define first electron affinity

Answer 16

the enthalpy change when one mole of gaseous atoms is converted into gaseous ions with a single negative charge.

Question 17

give an equation to express the first electron affinity of chlorine

Answer 17

Cl(g) + e- → Cl-(g)

Question 18

Define second electron affinity

Answer 18

The enthalpy change when one mole of gaseous 1- ions is converted into one mole of gaseous ions with a double negative charge.

Question 19

Give an equation to express the second electron affinity pf oxygen

Answer 19

O-(g) + e- → O2-(g)

Question 20

In gaseous elements such as oxygen and chlorine, which two enthalpy values can be equated?

Answer 20

enthalpy of atomisation and bond dissociation enthalpy

Question 21

What enthalpy changes are exothermic?

Answer 21

enthalpy of formation

first electron affinity

Question 22

what enthalpy changes are endothermic?

Answer 22

lattice enthalpy
enthalpy of atomisation
bond dissociation enthalpy
first ionisation energy
second ionisation energy

Question 23

what does a +ve ∆H imply?

Answer 23

endothermic enthalpy change

Question 24

what goes a -ve ∆H imply?

Answer 24

exothermic enthalpy change

Question 25

Describe the enthalpy changes found clockwise in an enthalpy diagram

Answer 25

``` TOP -> BOTTOM - Electron affinities - Lattice enthalpy BOTTOM -> TOP - Enthalpy of formation - Enthalpy of atomisation - Ionisation energies - Bond dissociation enthalpy (or atomisation) ```

Question 26

what does a large endothermic enthalpy value mean?

Answer 26

there is a large electrostatic force of attraction between the oppositely charged ions, therefore the bonds are very strong

Question 27

What factors govern the size of lattice enthalpy?

Answer 27

ionic size | ionic charge

Question 28

how does ionic size govern the size of lattice enthalpy?

Answer 28

Lattice enthalpy becomes less endothermic (less positive) as the size of the negative ion increases. This indicates weaker attraction between ions and hence weaker ionic bonding

Question 29

how does ionic charge govern the size of lattice enthalpy?

Answer 29

Charge increases and produces a greater attraction between these positive ions and negative ions. The ionic radius decreases, resulting in the ions in the lattice being closer together, producing more attraction. Therefore as charge increases, lattice enthalpies become more endothermic, therefore more positive.

Question 30

what types of compounds would you expect to have the most positive lattice enthalpies?

Answer 30

those with small, highly charged ions

Question 31

define enthalpy of solution

Answer 31

The enthalpy change when one mole of a solute dissolves in water.

Question 32

define enthalpy of hydration

Answer 32

The enthalpy change when one mole of gaseous ions is converted to one mole of aqueous ions.

Question 33

What processes occur when an ionic solid dissolves and why?

Answer 33

1. breakdown of the ionic lattice - overcoming the attractive forces requires energy 2. Hydration of the gaseous ions - gaseous ions bond with the water molecules

Question 34

What equation connects enthalpy of solution and enthalpy of hydration?

Answer 34

Enthalpy of solution = lattice enthalpy + enthalpy of hydration