chapter 22

Question 1

What is lattice enthalpy?

Answer 1

The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.
Also a measure of the strength of the ionic bonds in the compound.

Question 2

What is the Bourn-Haber cycle?

Answer 2

A way of measuring the lattice enthalpy as it cannot be directly measured

Question 3

What are the steps included in the Born-Haber cycle?

Answer 3

Gaseous ions
Solid ionic lattice
Elements in standard states
Gaseous atoms

Question 4

What is the enthalpy change of atomisation?

Answer 4

The enthalpy change that occurs when one mole of gaseous atoms is formed from the element in its standard state.
Always endothermic.

Question 5

What is first ionisation enthalpy?

Answer 5

The enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
Always endothermic.

Question 6

What is the first electron affinity?

Answer 6

The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.
Always exothermic

Question 7

What happens if the positive ion has a charge greater than 1+ ?

Answer 7

They will have to have successive ionisation enthalpies which are always endothermic

Question 8

What happens to the ion is it has a charge greater than 1-

Answer 8

They will need successive electron affinities which are always endothermic

Question 9

What is the enthalpy change of solution?

Answer 9

The enthalpy change that occurs when one mole of a solute dissolves completely in a solvent, water.

Question 10

How is the enthalpy change of solution calculated?

Answer 10

Experimentally, by measuring the temperature when the solute forms a solution.

Question 11

How do you dissolve ionic compounds?

Answer 11

Water molecules form strong enough bonds to break up the giant ionic lattice and overcome the strong electrostatic attractions between the oppositely charged ions.

Question 12

What is the enthalpy change of hydration?

Answer 12

The enthalpy change that accompanies the dissolving of gaseous ions to form i mole of aqueous ions.
Always exothermic.

Question 13

What happens when the enthalpy change of solution is endothermic?

Answer 13

The magnitude of the lattice enthalpy is greater than the magnitude of the sum of the hydration enthalpies.

Question 14

What happens when the enthalpy change of solution is exothermic?

Answer 14

The magnitude of the lattice enthalpy is smaller than the magnitude of the sum of the hydration enthalpies.

Question 15

What does the values of lattice enthalpies depend on?

Answer 15

Ionic size
Ionic charge

Question 16

What effect does ionic size have on the lattice enthalpy? (Down a group)

Answer 16

Ionic radius increases
Attraction between oppositely charged ions decreases
Lattice enthalpy less exothermic
Melting point decreases

Question 17

What effect does ionic charge have on lattice enthalpy? (Across a period)

Answer 17

Ionic charge increases
Attraction between oppositely charged ions increases
Lattice enthalpy more exothermic
Melting point increases.

Question 18

What factors affect hydration enthalpies?

Answer 18

Ionic size
Ionic charge

Question 19

What is the effect of ionic size on hydration enthalpy? (Down a group)

Answer 19

Ionic radius decreases
Attraction between ion and water molecules decreases
Hydration enthalpy less exothermic

Question 20

What is the effect of ionic charge on hydration enthalpy? (Across a period)

Answer 20

Ionic charge increases
Attraction between ion and water molecules increases
Hydration enthalpy more exothermic

Question 21

How do you predict the solubility of a compound?

Answer 21

If the enthalpy change of solution is exothermic, the compound will be soluble

Question 22

What is entropy?

Answer 22

A measure of the dispersal of energy and disorder within the chemicals making up the chemical system.

Question 23

What happens to the entropy when a substance changes from solid to liquid to gas?

Answer 23

The randomness of particles increases which means energy spreads out more and the change in entropy is positive

Question 24

What does the production of a gas do to the disorder of the particles?

Answer 24

The disorder will increase when a gas is produced

Question 25

What does a decrease in moles do to the randomness of particles?

Answer 25

The randomness will decrease

Question 26

How do you calculate entropy change?

Answer 26

enthalpy change of products - enthalpy change of reactants

Question 27

What is free energy?

Answer 27

The overall change in energy during a chemical reaction or process.

Question 28

What types of energy does free energy take into account?

Answer 28

The enthalpy change The dispersal of energy

Question 29

What is Gibbs' equation?

Answer 29

ΔG = ΔH − TΔS

Question 30

When is a reaction feasible?

Answer 30

When G is negative

Question 31

What are the limitations to the free energy equation?

Answer 31

Sometimes reactions have a negative G value but do not tale place. The equation takes no account of the kinetics/rate of the reaction. If the activation energy is high, the reaction will be too slow and will not take place.