Energetics II

Question 1

Define standard lattice energy?

Answer 1

Enthalpy change when 1 mol of an Ionic lattice is formed from isolated gaseous atoms under standard conditions

Question 2

What does standard lattice energy show?

Answer 2

Is a measure of Ionic bond strength
The more negative the lattice energy the stronger the bond

Question 3

Explain how Ionic charge and size affects lattice energy?

Answer 3

The higher the charge on the ions,the more energy is released when an Ionic lattice forms
This is due to stronger electrostatic forces of attraction
The smaller the Ionic radius of ions involved,the more exothermic the lattice energy is

Question 4

Define standard enthalpy of hydration?

Answer 4

The enthalpy change when one mole of aqueous ions are formed from their gaseous ions under standard conditions
E.g K+(g)+H20>K+(aq)

Question 5

Explain whether standard enthalpy of hydration is endo or exo?

Answer 5

Exothermic-as making bonds is an exothermic process

Question 6

Define standard enthalpy of solution?

Answer 6

The enthalpy change when one mole of an Ionic substance dissolves in water

Question 7

Explain what happens when an Ionic substance dissolves in water?

Answer 7

Ionic lattice breaks down into gaseous ions
Ions are hydrated(enthalpy of hydration)

Question 8

Explain how to calculate enthalpy change of solution?

Answer 8

This is:
Enthalpy change of hydration-enthalpy change of lattice

Question 9

What does it mean if ECOS is less than 0?

Answer 9

This means it’s exothermic and the energy required to separate the solute into its constituent ions is less than the energy given off when ions are hydrated
Use the equation

Question 10

Explain what happens if ECOS is greater than 0?

Answer 10

This is endothermic and the amount of energy required to separate the solute into constituent ions is greater than energy given off when ions are hydrated

Question 11

How does Ionic size/radius affect hydration enthalpy?

Answer 11

The smaller the size of ions the greater the enthalpy of hydration-This is because small ions exert more attraction on water molecules and more energy is released when hydrated.

Question 12

How does Ionic charge affect hydration enthalpy?

Answer 12

As charge on the ions increases it has a greater attraction for water molecules
This is because more highly charged ions exert more attraction on water molecules and more energy is released when these are hydrated

Question 13

What is the difference between theoretical ECOL and experimental ECOL?

Answer 13

Some Ionic compounds have covalent characteristics
Theoretical ECOL does not account for this whereas experimental does
This means theoretical is less exothermic that experimental

Question 14

Explain the factors affecting covalent character in Ionic compounds?

Answer 14

The higher the charge of the cation-the greater polarising power so more covalent character
The smaller the ion the greater charge density so more polarising
The greater the size the more polarisable it is

Question 15

Why is the hydration enthalpy of H+ ions very large?

Answer 15

Very small as it has one electron shell so small Ionic radius
Small ions exert more attraction so more energy is released

Question 16

Explain how Standard enthalpy of solution is linked with solubility?

Answer 16

If enthalpy change of solubility is negative(exothermic)than it is soluble

If it is slightly endothermic for example between 0-10KJ per mol it is also soluble