Lattice Enthalpy

Question 1

What is lattice enthalpy?

Answer 1

(A measure of the strength of the strength of the ionic bonding in a lattice)
The enthalpy change when one mole of an ionic lattice is formed from gaseous ions.

Question 2

What affects lattice enthalpy?

Answer 2

Ionic size, radius and charge.
Smaller, more charged ions produce larger lattice enthalpy (more negative).
Larger ions have a more spread out charge and are further apart, decreasing electrostatic forces of attraction between oppositely charged ions.
(I think this is because when the bond is made, less energy is released into the surroundings, making the reaction less exothermic, meaning lattice enthalpy is smaller, aka more positive)

Question 3

What are the two ways of calculating lattice enthalpy?

Answer 3

Born Haber Cycle or enthalpy cycle (dissolving in water)

Question 4

Is lattice enthalpy endothermic or exothermic? What direction does its arrow point in a born Haber cycle?

Answer 4

Exothermic as bonds are made. As a result the arrow points down.

Question 5

What is enthalpy change of formation?

Answer 5

(ΔHfꝋ) is the enthalpy change when 1 mole of a compound is formed from its elements under standard conditions (100KPa and 298K)

Question 6

Is enthalpy of formation endothermic or exothermic?

Answer 6

Exothermic. It involves the making of bonds. Therefore, its arrow points down to the ionic compound in a born Haber cycle.

Question 7

What is ionisation enthalpy?

Answer 7

(ΔHieꝋ) of an element is the amount of energy required to remove an electron from onw mole of a gaseous atom of an element to form a gaseous ion under standard conditions

Question 8

What is the standard enthalpy change of atomisation?

Answer 8

(ΔHatꝋ) is the enthalpy change when 1 mole of gaseous atoms is formed from its element under standard conditions

Question 9

Is enthalpy change of atomisation endothermic or exothermic?

Answer 9

Endothermic because bonds are being broken in the element to produce gaseous atoms. So its arrow points down.

Question 10

What is standard enthalpy of electron affinity?

Answer 10

(ΔHeaꝋ) The enthalpy change when one mole of electrons is added to a mole of gaseous atoms to form one mole of gaseous 1- ions under standard conditions.

Question 11

What is the order of enthalpies in a born haber cycle?

Answer 11

Formation, atomisation, ionisation and then electron affinity.

Question 12

What is enthalpy change of solution?

Answer 12

This is the enthalpy change when one mole of an ionic lattice dissolves in sufficient water to form an infinitely dilute solution.
KCl(s) + aq —> K+ (aq) + Cl- (aq)
It can be endothermic or exothermic

Question 13

What is the enthalpy change of hydration?

Answer 13

The enthalpy change when one mole of gaseous ions dissolves in water to form an infinitely dilute solution.
Mg2+(g) + aq → Mg2+(aq)

Question 14

What factors affect enthalpy of hydration.

Answer 14

Ionic size, radius and charge.
Smaller, more charged ions have a greater hydration enthalpy. It will be much more negative.
Larger ions have a more spread out charge and are further apart, decreasing electrostatic forces of attraction between oppositely charged ions.