5.2.1 Lattice Enthalpy

Question 1

what is lattice enthalpy?

Answer 1

the enthalpy when one mole of a solid ionic lattice is formed from its gaseous ions under standard conditions

Question 2

is lattice enthalpy endo or exo?

Answer 2

exothermic as bonds are made (downward arrow)

Question 3

what is the enthalpy of atomisation?

Answer 3

the enthalpy change when one mole of gaseous atoms form from the elements in their standard states

Question 4

is enthalpy of atomisation endo or exo?

Answer 4

endothermic as bonds are broken (upwards arrow)

Question 5

is first ionisation energy endo or exo?

Answer 5

endothermic as attractions are overcome

Question 6

is the 2nd IE more endothermic than the first?

Answer 6

more endothermic as their are greater attractions

Question 7

what is the first electron affinity?

Answer 7

the enthalpy change when one electron is added to each atom in one mole of gaseous atoms, forming one mole of gaseous 1- ions

Question 8

is the 1st electron affinity endo or exo?

Answer 8

exothermic (bonds formed)

Question 9

is the 2nd electron affinity endo or exo?

Answer 9

endothermic as the repulsion between the negative ion and the negative electron has to be overcome

Question 10

why is lattice enthalpy always negative?

Answer 10

it is exothermic as energy is given out from forming electrostatic attractions form between ions

Question 11

what does more exothermic lattice enthalpy imply?

Answer 11

• more negative
• stronger electrostatic attractions
• stronger ionic bonds
• higher melting/boiling points

Question 12

which will have a more exothermic lattice enthalpy between NaCl and KCl?

Answer 12

• NaCl will be more exo
• Na+ ion is smaller and the same charge as the K+ ion
• greater charge density
• stronger attractions between ions
• Na+ and Cl- attracted to each other more strongly

Question 13

which will have a more exothermic lattice enthalpy between MgO and Na2O?

Answer 13

• MgO will be more exo
• Mg2+ has a higher charge and is a slightly smaller ion than Na+
• greater charge density
• stronger attractions between ions
• Mg2+ and O2- attracted to each other more strongly

Question 14

what is enthalpy change of solution?

Answer 14

the enthalpy change when one mole of a solute is completely dissolved in water under standard conditions

Question 15

what is the enthalpy change of hydration?

Answer 15

the enthalpy change when one mole of aqueous ions are formed from their gaseous ions under standard conditions

Question 16

is enthalpy of hydration endo or exo?

Answer 16

exothermic as attractions are being formed between the ions and water molecules

Question 17

what is the effect of ionic size on the enthalpy of hydration?

Answer 17

• smaller ion
• higher charge density
• so stronger attractions between ions and water molecules
• more exothermic enthalpy of hydration

Question 18

what is the effect of ionic charge on the enthalpy of hydration?

Answer 18

• higher charge on ion
• higher charge density
• so stronger attractions between ions and water

Question 19

how to calculate enthalpy of solution from Born-Haber diagram?

Answer 19

enthalpy of solution = - LE + sum of enthalpy of hydration
(multiply for multiple moles of ions in diagram)