Module 5 Chapter 22

Question 1

What are features of ionic compounds

Answer 1

They are very stable with high melting points

Question 2

What are ionic bonds

Answer 2

They are the strong electrostatic forces of attraction between oppositely - charged ions in the ionic lattice structure

Question 3

What is a feature of the energy that is required to break the lattice

Answer 3

There is a substantial energy barrier that has to be broken down in the lattice

Question 4

What is lattice enthalpy

Answer 4

A measure of the strength of ionic bonding in a giant ionic lattice

Question 5

What is lattice enthalpy

Answer 5

The enthalpy change due to the formation of 1mol of ionic lattice from gaseous ions (under standard conditions)

Question 6

What are features of lattice enthalpy

Answer 6

It provides a measure of ionic bonding strength
-It is always exothermic

Question 7

What is the standard enthalpy change of atomisation

Answer 7

It is the enthalpy change of forming 1mol of gaseous atoms from the element in its standard state under standard conditions

Question 8

What is a feature of standard enthalpy change of atomisation

Answer 8

It is always endothermic

Question 9

What is a feature of the standard enthalpy change of atomisation

Answer 9

If the elements is a gas this value is related to bond enthalpy

Question 10

What is first electron affinity

Answer 10

Is the enthalpy change when an electron is added to each atom in 1mol of gaseous atoms of -1 gaseous ions

Question 11

What is a feature of first electron affinity

Answer 11

It is always exothermic
Successive electron affinities are needed for greater charges

Question 12

Why are successive electron affinities endothermic

Answer 12

As the electron is repelled by the negative ion

Question 13

What is a feature of measuring lattice enthalpy

Answer 13

Lattice enthalpy can’t be measured directly, must be calculated - indirectly using known enthalpy changes in an energy cycle

Question 14

What is the standard enthalpy change of solution

Answer 14

It is the enthalpy change due to 1 mole of a solute dissolving in a solvent

Question 15

What is a feature of the enthalpy change of solution

Answer 15

It can be exothermic or endothermic

Question 16

What is the enthalpy change of hydration

Answer 16

It is the enthalpy change due to dissolving gaseous ions in water to form 1 mole of aqueous ions

Question 17

How the the enthalpy change of solution be calculated experimentally

Answer 17

BY recording the temperature change when adding an ionic compound to water

Question 18

What is the method for working out the enthalpy change of solution

Answer 18

1. Take the mass of one of the salts
2. Measure 50cm^3 of distilled water and add to a polystyrene cup and take its temperature
3. Add the salt to water and stir with the thermometer
4. Record the greatest temperature change

Question 19

What is the equation to calculate the enthalpy change of solution

Answer 19

Mass x specific heat capacity x change in temperature/ 1000 x moles

Question 20

What is the mass in the equation

Answer 20

It is the mass of the solute + the mass of the solvent

Question 21

What happens when an ionic compound dissolves

Answer 21

The ionic lattice breaks to form separate ions
—> therefore is opposite change from lattice enthalpy

The gaseous ions are attracted tot the polar water to become hydrated aqueous ions
—> energy change = enthalpy change of hydration

Question 22

How can you categorise whether the enthalpy change of solution is exothermic or endothermic

Answer 22

If the lattice enthalpy change is greater than the enthalpy change of hydration - endothermic

If the lattice enthalpy change is less than the enthalpy change of hydration - exothermic

Question 23

What determines whether an ionic compound is soluble or insoluble

Answer 23

The relative magnitude of lattice and hydration enthalpies helps to explain this variety.

Question 24

What do lattice enthalpy values depend on

Answer 24

ionic size and ionic charge

Question 25

What is the effect of ionic size

Answer 25

Ionic radius increases Attraction between ions decreases Lattice energy less negative Melting point decreases

Question 26

What is the effect of cation charge for similar sized cations on lattice enthalpy

Answer 26

Ionic charge increases Attraction between ions increases Lattice enthalpy becomes more negative Melting point increases

Question 27

What does the magnitude of lattice enthalpy tell you

Answer 27

It hints at the melting point of the ionic compound

Question 28

What does an exothermic lattice enthalpy tell you

Answer 28

It indicates a very high melting point —> the compound is therefore very stable —> useful as industrial materials

Question 29

How does ionic radius affect hydration enthalpy

Answer 29

As ionic radius increases the hydration enthalpy becomes less negative as the attraction between ions and water decreases.

Question 30

How does ionic charge affect hydration enthalpy

Answer 30

As ionic charge increases the hydration enthalpy becomes more negative as the attraction between ions and water increases

Question 31

What happens if hydration enthalpy is greater than lattice enthalpy

Answer 31

Then dissolving is likely to happen

Question 32

What is required for an ionic compound to dissolve

Answer 32

The attraction between ions within the lattice needs to be overcome The needs energy that is equivalent to the lattice enthalpy

Question 33

How can you determine if a substance is likely to dissolve from lattice

Answer 33

If the sum of the hydration enthalpies is larger than the magnitude of the lattice enthalpy —> enthalpy change is exothermic —> should dissolve

Question 34

Is this rule for dissolving always true

Answer 34

Some compounds have an endothermic change and are soluble

Question 35

Why is this rule for dissolving not always true

Answer 35

As solubility depends on temperature

Question 36

What is entropy

Answer 36

It is a measure of the dispersal of energy in a system, which increases as the system is more disorder

Question 37

What is ^S and its units

Answer 37

the change in entropy in J/KMol

Question 38

What do physical states have different levels of

Answer 38

Entropy due to the amount of ‘randomness’ of the particles

Question 39

What are the state changes when ^S is greater than 0

Answer 39

Solid —> liquid —> gase

Question 40

What are the state changes when ^S is less than 0

Answer 40

Gas —> liquid —> solid

Question 41

What occurs at 0K

Answer 41

there is no energy within the system, so entropy will have a value of 0 J/Kmol. All the system above 0K will have some energy dispersed within it, entropy will always have a positive value.

Question 42

What are the signs accompanying the different entropy changes

Answer 42

+S = increasing the disorder -S = decreasing the disorder

Question 43

What is the standard entropy

Answer 43

Is the entropy of one mole of a substance under standard conditions

Question 44

What is a feature of standard entropy

Answer 44

It always has a positive value and units of J/KMol

Question 45

How can the entropy change of a reaction be calculated

Answer 45

using standard entropies ^S = sum of S of products - sum of S of reactants

Question 46

What is the feasibility of a reaction used for

Answer 46

To determine if a reaction will be able to happen and is energetically feasible/spontaneous

Question 47

What is teh free energy change

Answer 47

It is the overall energy change

Question 48

What is the free energy change caused by (1)

Answer 48

Heat transfer between the system and surroundings (^H) (enthalpy change)

Question 49

What is the free energy change caused by (2)

Answer 49

Dispersal of energy within the system at the temperature of the reaction (T^S) (the entropy change at the temperature of the reaction)

Question 50

What is the gibbs equation

Answer 50

^G = ^H - T^S

Question 51

When is a reaction feasible

Answer 51

When ^G < 0

Question 52

What does the feasibility of a reaction depend on

Answer 52

The balance between ^H and T^S

Question 53

Why is the Gibbs equation not an accurate way to predict whether a reaction will take place (1)

Answer 53

As a negative G doesn’t mean that the reaction will take place As some reactions require a massive activation energy —> slow rate

Question 54

Why is the Gibbs equation not an accurate way to predict whether a reaction will take place (2)

Answer 54

^G indicates thermodynamic feasibility but does not take into account the kinetics or rate of reaction

Question 55

Draw the cycle for the enthalpy change of hydration, solution and lattice enthalpy

Answer 55

DRAW IT

Question 56

DRAW the born-haber enthalpy change cycle