Lattice Enthalpy

Question 1

Define lattice enthalpy?

Answer 1

The enthalpy change when one mole of an ionic compound is converted Into gaseous ions

Question 2

What is the trend in the lattice enthalpies of ionic compounds?

Answer 2

• lattice enthalpy decreases as metal ions get bigger
• lattice enthalpy increases as ion charge increases
• Group 2 fluorides lattH is greater then group 1 (greater attraction as charge on metal on increases)
• Group 2 oxides lattH is greater then group 2 fluorides as the oxide ion has a greater charge then the fluoride.

Question 3

Define the standard enthalpy of formation?

Answer 3

The enthalpy change when one mole of the compound is formed from it’s elements under standard conditions

Question 4

Define the enthalpy of atomisation?

Answer 4

The enthalpy change when one mole of gaseous ions is formed from the element in it’s standard state.

Question 5

Define the first election affinity?

Answer 5

The enthalpy change when one mole of gaseous atoms is converted into gaseous ions with a single negative charge

Question 6

Define first ionisation energy?

Answer 6

The energy required to convert one mole of gaseous atoms into gaseous ions with a single positive charge

Question 7

What’s the relationship between the electronegativity of an element and the first electron affinity?

Answer 7

EA 1 is very exothermic for electronegative elements (oxygen, fluorine) for less electronegative elements EA 1 is smaller

Question 8

Why is EA 2 endothermic?

Answer 8

Energy is required to overcome the repulsion when an electron is added to a negatively charged ion.

Question 9

Define second ionisation energy?

Answer 9

The energy required to convert one mole of a gaseous ions with a single positive charge into gaseous ions with a double positive charge

Question 10

Define bond dissociation enthalpy?

Answer 10

The energy required to break one mole of a covalent bond under standard conditions

Question 11

What is the equation for lattice enthalpy?

Answer 11

LattH = Enthalpy (Atomisation, Ionisation, Electron affinity) - Formation enthalpy

Question 12

Define enthalpy of solution?

Answer 12

The enthalpy change when one mole of a solute dissolves in water

Question 13

Define the enthalpy of hydration?

Answer 13

The enthalpy change when one mole of gaseous ions is converted to one mole of aqueous ions

Question 14

What is the equation for the enthalpy of solution?

Answer 14

Enthalpy of solution = lattice enthalpy + hydration enthalpy

Question 15

What happens when a ionic compound dissolves in water (magnesium chloride)

Answer 15

The magnesium and chloride ions break from the solid forming bonds with water molecules which forms a solvated ion resulting in ion-dipole bonds

Question 16

Why is lattice enthalpy endothermic?

Answer 16

Energy is needed to overcome the attractive forces between oppositely charged ions in the lattice

Question 17

Why is formation exothermic?

Answer 17

Energy released when the ions bond and form the lattice is greater than the energy needed to break bonds in the elements.

Question 18

Is the enthalpy of atoms and ions exothermic or endothermic?

Answer 18

Atoms are endomermic as energy is needed to overcome the attractive forces between oppositely charged ions in the Latrice.

Ions are mostly endothermic as the energy needed to ionise the metal atoms is greater than the energy released on adding electrons to the non-metal atoms.

Question 19

If a reaction is endothermic or exothermic is the lattice enthalpy positive or negative?

Answer 19

If exothermic enthalpy is negative
Endothermic enthalpy is positive