3.1.8 Thermodynamics

Question 1

3.1.8.1 Born-Haber cycles

Define enthalpy of formation.

Answer 1

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

Exothermic (-ve) for most substances

Question 2

3.1.8.1 Born-Haber cycles

Define first ionisation energy.

Answer 2

Enthalpy change when each atom in 1 mole of gaseous atoms loses 1 electron to form 1 mole of gaseous 1+ ions.

Endothermic (+ve)

Question 3

3.1.8.1 Born-Haber cycles

Define second ionisation energy.

Answer 3

Enthalpy change when each ion in 1 mole of gaseous 1+ ions loses 1 electron to form 1 mole of gaseous 2+ ions.

Endothermic (+ve)

Question 4

3.1.8.1 Born-Haber cycles

Define enthalpy of atomisation.

Answer 4

Enthalpy change when 1 mole of gaseous atoms is produced from an element in its standard state.

Endothermic (+ve) → 1/2 I2 (s)→I (g)

Question 5

3.1.8.1 Born-Haber cycles

Outline an example of enthalpy of atomisation.

Answer 5

½ I (s) →I (g)

Question 6

3.1.8.1 Born-Haber cycles

Define bond enthalpy.

Answer 6

Enthalpy change when 1 mole of covalent bonds is broken in the gaseous state.

Endothermic (+ve)

Question 7

3.1.8.1 Born-Haber cycles

Outline an example of enthalpy of formation.

Answer 7

2Na(s) + 1/2O2(g) →Na2O(s)

Question 8

3.1.8.1 Born-Haber cycles

Outline an example for the first ionisation energy.

Answer 8

Mg(g) →Mg+ + e-

Question 9

3.1.8.1 Born-Haber cycles

Outline an example for the second ionisation energy.

Answer 9

Mg+(g) →Mg2+(g) + e-

Question 10

3.1.8.1 Born-Haber cycles

Outline an example of bond enthalpy.

Answer 10

I2 (g) →2I (g)

Question 11

3.1.8.1 Born-Haber cycles

Define the first electron affinity.

Answer 11

When each atom in 1 mole of a gaseous atoms gains 1 electron to form 1 mole of gaseous 1- ions.

Exothermic (-ve) for many metals.

Question 12

3.1.8.1 Born-Haber cycles

Outline an example for the first electron affinity.

Answer 12

O (g) + e- → O-(g)

Question 13

3.1.8.1 Born-Haber cycles

Define the second electron affinity.

Answer 13

Enthalpy change when each ion in one mole of gaseous 1- ions gains 1 electron to form one mole of gaseous 2- ions.

Endothermic (+ve) as adding -ve electron to a -ve ion = +

Question 14

3.1.8.1 Born-Haber cycles

Outline an example for the second electron affinity.

Answer 14

O- (g) + e- →O2- (g)

Question 15

3.1.8.1 Born-Haber cycles

Define lattice enthalpy.

Answer 15

can be defined as either enthalpy of lattive dissociation or enthalpy of lattice formation.

Question 16

3.1.8.1 Born-Haber cycles

Define lattice enthalpy of formation.

Answer 16

Enthalpy change when 1 mole of a solid ionic compound is formed into its consituent ions in gas phase.

Exothermic (-ve)

Question 17

3.1.8.1 Born-Haber cycles

Outline an example of lattice enthalpy of formation.

Answer 17

Mg2+ (g) + 2Cl- (g)→MgCl2 (s)

Question 18

3.1.8.1 Born-Haber cycles

Define lattice enthalpy of dissociation.

Answer 18

Enthalpy change when 1 mole of a solid ionic compound is broken up into its consituent ions in gas phase.

Endothermic (+ve)

Question 19

3.1.8.1 Born-Haber cycles

Outline an example of lattice enthalpy of dissociation.

Answer 19

MgCl2 (s) →Mg2+ (g) + 2Cl- (g)

Question 20

3.1.8.1 Born-Haber cycles

Define the enthalpy of hydration.

Answer 20

Enthalpy change when 1 mole of gaseous ions become aqueous ions / hydrated.

Exothermic (-ve), gives out energy as bonds are made between ion and H2O

Question 21

3.1.8.1 Born-Haber cycles

Outline an example of enthalpy of hydration.

Answer 21

Mg2+ (g) + aq→Mg2+(aq)

Question 22

3.1.8.1 Born-Haber cycles

Define enthalpy of solution.

Answer 22

Standard enthalpy change when one mole of an ionic solid dissolves in a large enough amount of water to ensure that the dissolved ions are well separated and do not interact with one another.

Question 23

3.1.8.1 Born-Haber cycles

Outline an example of enthalpy of solution.

Answer 23

MgCl2 (s)