Topic 15.1: Energy cycles

Question 1

Definition of Born-Haber cycle

Answer 1

Energy cycles describing the formation of ionic compounds

Question 2

Can lattice enthalpy be measured directly?

Answer 2

It cannot be measured because gaseous ions do not combine directly to form a compound

Question 3

Enthalpy changes involved in the Born-Haber cycle

Answer 3

a) Enthalpy of formation
b) Enthalpy of atomization
c) First ionization energy
d) Second ionization energy
e) First electron affinity
f) Second electron affinity
g) Lattice enthalpy

Question 4

Definition of first ionization energy

Endothermic

Answer 4

Enthalpy change when one electron is removed from each atom in one mole of gaseous atoms under standard conditions

Question 5

Definition of second ionization energy

Endothermic

Answer 5

Enthalpy change when one electron is removed from each ion in one mole of gaseous ions under standard conditions.

Question 6

Definition of first electron affinity

Exothermic

Answer 6

Enthalpy change when one electron is added to each atom in one mole of gaseous atoms under standard conditions

Question 7

Definition of second electron affinity

Endothermic

Answer 7

Enthalpy change when one electron is added to each ion in one mole of gaseous ions under standard conditions

Question 8

Definition of atomization enthalpy

(Endothermic

Answer 8

Enthalpy change when one mole of gaseous atoms is formed from an element under standard conditions

Question 9

Definition of lattice enthalpy

Endothermic

Answer 9

Enthalpy change when one mole of an ionic compound is broken apart into its gaseous ions under standard conditions

Question 10

Definition of hydration enthalpy

Exothermic

Answer 10

Enthalpy change when one mole of gaseous ions is surrounded by water molecules to form an infinitely dilute solution under standard conditions

Question 11

Definition of enthalpy of solution

Endothermic / Exothermic

Answer 11

Enthalpy change when one mole of solute is dissolved in excess solvent to form a infinitely dilute solution under standard conditions

Question 12

Factors affecting the magnitude of lattice and hydration enthalpy values

Answer 12

a) Ionic radius

b) Charge

Question 13

Ionic radius

a) Lattice enthalpy
b) Enthalpy of hydration

Answer 13

a) The smaller the ions, the closer they are together and the stronger the forces of attraction between oppositely charged ions so, the greater the lattice enthalpy
b) Smaller ions are more exothermic because of a stronger electrostatic attraction between the ion and water molecules

Question 14

Charge

a) Lattice enthalpy
b) Enthalpy of hydration

Answer 14

a) The greater the charge on the ions, the stronger the forces of attraction between oppositely charged ions; so, the greater the lattice enthalpy
b) More highly charged ions are more exothermic because of a stronger electrostatic attraction between the ion and water molecules

Question 15

Assumption of lattice enthalpy

Answer 15

Compound is 100% ionic
If the experimental and theoretical lattice enthalpy do not agree, the ionic structure contains some degree of covalent character

Question 16

Type of reaction

a) Hydration enthalpy > Lattice enthalpy
b) Hydration enthalpy < Lattice enthalpy
c) Hydration enthalpy &laquo_space;Lattice enthalpy

Answer 16

a) Exothermic dissolution
b) Endothermic dissolution
c) No dissolving