P- Born-Haber Cycles + all enthalpy defs

Question 1

Enthalpy of formation

Answer 1

• enthalpy change
• when 1 mole of a substance is formed from its constituent elements
• all substances in their standard states
• exo for most

Question 2

Enthalpy of neutralisation

Answer 2

• enthalpy change
• when 1 mole of H2O is formed in a reaction betw an acid + alkali
• under standard conditions
• exo

Question 3

First ionisation energy

Answer 3

The energy required to remove 1 mole of electrons from 1 mole of atoms in the gaseous state.
- endo

Question 4

Second ionisation energy

Answer 4

The energy required to remove 1 mole of electrons from 1 mole of gaseous 1+ ions.
- endo

Question 5

First electron affinity

Answer 5

• enthalpy change
• when each atom in 1 mole of gaseous atoms gains 1 e-
• to form 1 mole of gaseous 1- ions
• exothermic

Question 6

Second electron affinity

Answer 6

• enthalpy change
• when each ion in 1 mole of gaseous 1- ions gains 1 e-
• to form 1 mole of gaseous 2- ions
• endothermic (adding -ve e- to -ve ion)

Question 7

Enthalpy of atomisation

Answer 7

• enthalpy change
• when 1 mole of gaseous atoms is produced from
• an element in its standard state
• endothermic

Question 8

Hydration enthalpy

Answer 8

• enthalpy change
• when 1 mole of gaseous ions become hydrated (dissolved in H2O)
• exo

Question 9

Enthalpy of solution

Answer 9

• enthalpy change
• when 1 mole of an ionic solid dissolves
• in an amount of water large enough so that the dissolved ions are well separated + x interact w/ each other
• can be exo/ endo

Question 10

Bond dissociation enthalpy

Answer 10

• enthalpy change
• when 1 mole of covalent bonds is broken
• in the gaseous state
• endothermic

Question 11

Lattice enthalpy of formation

Answer 11

• enthalpy change
• when 1 mole of a solid ionic compound is formed
• from its constituent ions
• in the gas phase
• exo

Question 12

Lattice enthalpy of dissociation

Answer 12

• enthalpy change
• when 1 mole of solid ionic compound is broken up
• into its constituent ions
• in the gas phase
• endothermic

Question 13

Enthalpy of vaporisation

Answer 13

• enthalpy change
• when 1 mole of a liquid is turned into a gas

Question 14

Enthalpy of fusion

Answer 14

• enthalpy change
• when 1 mole of a solid is turned into liquid

Question 15

What forces form between ions and polar water molecules when ions dissolve in water?

Answer 15

ion-dipole forces
- formation = exo

Question 16

What is the magnitude of lattice enthalpy a measure of?

Answer 16

strength of ionic bonding

Question 17

2 characteristics of ions that cause stronger attractions

Answer 17

1. smaller ions
2. ↑ +ve charged ions

Question 18

What does a more negative value of enthalpy of solution indicate about solubility of the substance?

Answer 18

↑ exo ↑ soluble

Question 19

2 reasons why substances are insoluble

Answer 19

1. v strong ionic bonding –> high lattice enthalpy
2. covalent (eg. diamond)

Question 20

How does comparing theoretical and experimental lattice enthalpies show the type of bonding in a substance?

Answer 20

↑ diff betw the values
↑ covalent character

Question 21

Assumptions made by the perfect ionic model

Answer 21

1. all ions- completely spherical
2. all ions- even charge distribution
3. attractions- purely electrostatic
4. x covalent character