5.2.1 + 5.2.2 energy

Question 1

Enthalpy change of formation

Answer 1

Enthalpy change when 1 mole of a compound is formed from its elements under standard conditions (298k, 100kPa), when reactants and products are in their standard states

Na(s) + 1/2 Cl2 (g) > NaCl (s)

Exothermic

Question 2

Enthalpy of atomisation

Answer 2

Enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state

1/2 O2 (g) > O (g)
Na (s) > Na (g)

Endothermic

Question 3

Enthalpy of sublimation

Answer 3

Enthalpy change when 1 mole of a solid metal turns to gaseous atoms

Same as atomisation

Na (s) > Na (g)

Endothermic

Question 4

First ionisation energy

Answer 4

Enthalpy change required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous ions with a +1 charge

Mg (g) > Mg+ (g) + e-

Question 5

Second ionisation energy

Answer 5

Enthalpy change required to remove 1 mole of electrons from one mole of gaseous 1+ ions to produce 1 mole of gaseous 2+ ions

Mg+ (g) > Mg2+ + e-

Question 6

First electron affinity

Answer 6

Enthalpy change required when 1 mole of gaseous atoms gain 1 mole of electrons to form 1 mole of gaseous ions with a -1 charge

Exothermic as ion is more stable than atom, attraction between nucleus and electron

O (g) + e- > O- (g)

Question 7

Second electron affinity

Answer 7

Enthalpy change required when 1 mole of gaseous -1 ions gain 1 electron per ion to produce -2 ions

Endothermic as it takes energy to overcome repulsive forces between negative ion and electron

Question 8

Lattice enthalpy

Answer 8

Enthalpy change when 1 mole of an ionic crystal lattice is formed from its constituent ions in gaseous form

Exothermic

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

Measure of ionic bond strength

Question 9

Enthalpy of hydration

Answer 9

Enthalpy change when 1 mole of gaseous ions become aqueous ions

Exothermic as bonds made between ions and water molecules

Question 10

Enthalpy of solution

Answer 10

Enthalpy change when 1 mole of an ionic solid dissolves in a large amount of water to ensure that dissolved ions are well separated and don’t interact with one another

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

Question 11

Born haber list

Answer 11

Formation - points Down

Atm, ionisation, atm ] - up

Ea - points down

Lattice enthalpy at end goes down

Question 12

Factors affecting lattice enthalpy

Answer 12

Size of ions
- the larger the ion, the less negative the enthalpies of lattice formation. As ions are larger the charges become further apart so have a weaker attractive force between them

Charges on the ion
- the bigger the charge, the greater the attraction between ions so stronger the lattice enthalpy (more neg)