5.2.1- Lattice Enthalpy

Question 0

Is lattice enthalpy endo or exothermic

Answer 0

Lattice enthalpies are always negative (it is an exothermic process because bonds are made). The more negative (more exothermic), the stronger the ionic bonds.

Question 1

Define Lattice enthalpy (ΔHLE)

Answer 1

The enthalpy change that accompanies the formation of one mole of an
ionic compound from its gaseous ions (under standard conditions)

Question 2

Define the standard enthalpy change of formation

Answer 2

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

Question 3

Define standard enthalpy change of atomisation

Answer 3

The enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state

Question 4

Define first ionisation energy

Answer 4

The enthalpy change when one electron is removed from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

Question 5

Define second ionisation energy

Answer 5

The enthalpy change when one electron is removed from each atom in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

Question 6

Define the first electron affinity

Answer 6

The enthalpy change when one electron is gained by each atom in one mole of gaseous atoms (to form one mole of gaseous 1- ions)

Question 7

Define second electron affinity

Answer 7

The enthalpy change when one electron is gained by each ion in one mole of gaseous 1- ions (to form one mole of gaseous 2- ions)

Question 8

Why can’t lattice enthalpies be determined experimentally

Answer 8

They cannot be measured directly because it is impossible to use gaseous ions to form one mole of an ionic lattice experiment

Question 9

Is the enthalpy change of atomisation endothermic or exothermic?

Answer 9

Always endothermic because bonds have to be broken

Question 10

Are ionisation energies endothermic or exothermic?

Answer 10

Always endothermic because the electron that has been lost has to overcome attraction from the nucleus in order to leave the atom

Question 11

Is the first electron affinity endothermic or exothermic?

Answer 11

Exothermic because the electron is attracted into the outer shell of the atom by the nucleus

Question 12

Is the second electron affinity endothermic or exothermic?

Answer 12

Endothermic because the electron is repelled by the 1- charge of the ion. This repulsion has to be overcome.

Question 13

Defined the enthalpy change of solution

Answer 13

The enthalpy change that takes place when one mole of a compound is completely dissolved in water
Eg. KCl (s) + aq-> K+ (aq) + Cl- (aq)

Question 14

What two processes take place when an ionic solid dissolves in water

Answer 14

1. Breakdown of ionic lattice into gaseous irons

2. Hydration of the ions

Question 15

What is the breakdown of the ionic lattice equal to

Answer 15

The positive version of the lattice enthalpy

Question 16

Define the enthalpy change of hydration

Answer 16

The enthalpy change for forming 1 mole of aqueous ions from 1 mole of gaseous ions

Question 17

What is two factors affect lattice enthalpies?

Answer 17

LE are affected by (i) ionic radius: there is a greater attraction between smaller ions and so lattice enthalpies become more negative as ionic radius decreases (ii) ionic charge: there is a greater attraction between ions with higher charges and so lattice enthalpies become more negative as ionic charge increases.