LATTICE

Question 1

Lattice energy

Answer 1

is the enthalpy change when 1 mole of an ionic compound is formed from
its gaseous ions under standard conditions

Question 2

The lattice energy is always

Answer 2

exothermic; the more exothermic the lattice energy, the
stronger the ionic bonding in the lattice

Question 3

The standard enthalpy change of atomisation,

Answer 3

∆HꝊ
at, is the enthalpy change when 1 mole
of gaseous atoms is formed from its element under standard conditions; is endothermic

Question 4

The first electron affinity, ∆HꝊ
ea1,

Answer 4

, is the enthalpy change when 1 mole of electrons is
added to 1 mole of gaseous atoms to form 1 mole of gaseous 1- ions under standard
conditions; is exothermic

Question 5

The second electron affinity, ∆HꝊ
ea2,

Answer 5

is the enthalpy change when 1 mole of electrons is
added to 1 mole of gaseous 1– ions to form 1 mole of gaseous 2– ions under standard
conditions; is endothermic – so are the 3rd electron affinities

Question 6

Answer 6

Question 7

Answer 7

Question 8

 Mg2+ requires

Answer 8

1st and 2nd ionisation energy to be calculated

Question 9

Two chloride ions in MgCl2,

Answer 9

hence the values of ∆HꝊ
at & ∆HꝊ
ea1 should be multiplied
by 2

Question 10

Lattice energy arises from the

Answer 10

electrostatic force of attraction of oppositely charged ions
when the crystalline lattice is formed

Question 11

As the size of the ion

Answer 11

increases, the lattice energy becomes less exothermic, e.g. the lattice
energy gets less exothermic as the size of the anion increases from F- to I-

Question 12

why does as the size of the ion increases
the lattice energy becomes less exothermic

Answer 12

Due to the decrease in charge density with the same ionic charge, as the same
charge is spread over a larger volume, resulting in weaker electrostatic forces of
attraction in the ionic lattice, e.g. NaF has a less exothermic lattice energy than LiF

Question 13

The lattice energy becomes more exothermic (stronger ionic bonds formed) as the

Answer 13

ionic
charge increases (higher charge density), e.g. LiF < MgO:

Question 14

The positive charge on the cation in an ionic lattice may attract

Answer 14

the electrons in the anion
towards it, resulting to distortion of the electron cloud of the anion, causing it to no longer
be spherical (ion polarisation)

Question 15

polarising power of the cation

Answer 15

the ability of a cation to attract electrons and distort an
anion

Question 16

The degree of polarisation on an anion depends on:

Answer 16

The degree of polarisation on an anion depends on:

Question 17

And more polarised if:

Answer 17

 The cation is small
 The cation has a charge of 2+ or 3+
 The anion is large
 The anion has a charge of 2- or 3-

Question 18

Many ionic bonding have some

Answer 18

covalent character due to ion polarisation

Question 19

The Group 2 carbonates decompose to

Answer 19

their oxides and carbon dioxide on heating:

Question 20

Answer 20

Question 21

The further down the group,

Answer 21

the higher temperature required to decompose the carbonate

Question 22

Answer 22

their relative stabilities increases down the group:

Question 23

Ion polarisation of carbonates:

Answer 23

The ionic carbonate ion has large ionic radius, hence easily polarised (given a small
highly charged cation)
 Group 2 cations’ ionic radius increase down the group:

Question 24

Answer 24

The smaller the ionic radius of the cation, the better the polarising power, hence
degree of polarisation of carbonate ion by Group 2 cation follows:

Question 25

Answer 25

The greater the polarisation, the easier it is to weaken a C – O bond in the carbonate and form the CO2 and oxide on heating

Question 26

Thermal decomposition of Group 2 nitrates has a similar pattern, decompose to form nitrogen dioxide, oxygen and the oxide:

Answer 26

Question 27

The enthalpy change of solution, ∆HꝊ sol,

Answer 27

is the energy when 1 mole of an ionic solid dissolve in sufficient water to form a very dilute solution; can be exothermic and endothermic

Question 28

Ion-dipole bonds are formed when

Answer 28

ionic solid dissolves in water:

Question 29

The enthalpy change of hydration, ∆HꝊ hyd,

Answer 29

is the enthalpy change when 1 mole of a gaseous ion dissolves in sufficient water to form a very dilute solution; is exothermic

Question 30

enthaly change for hydration is more exothermic when

Answer 30

 More exothermic for ions with the same charge but smaller ionic radii, e.g. ∆HꝊ hyd is more exothermic for Li+ than for Na+  More exothermic for ions with the same radii but a larger charge, e.g. ∆HꝊ hyd is more exothermic for Mg2+ than for Li+.

Question 31

Answer 31

Question 32

The solubility of Group 2 sulfates decreases as the

Answer 32

radius of the metal ion increases

Question 33

Change in hydration enthalpy down the group:

Answer 33

 Smaller ions (with same charge) have greater enthalpy changes of hydration  So the enthalpy change of hydration decreases (gets less exothermic) following:

Question 34

Answer 34

 hydration enthalpy Decrease is large down the group, depending entirely on the increase in size of the cation, as the anion is unchanged  Lattice energy is inversely proportional to the sum of the radii (cation & anion)  Sulfate ion much larger than group 2 cations, hence it contributes a greater part to the change in lattice energy down the group  Hence decrease in lattice energy is small down the group, determined more by the size of the sulfate ions than the size of the cations

Question 35

Change in lattice energy down the group:

Answer 35

 Smaller ions form greater lattice energy  So the lattice energy decreases following:

Question 36

The lattice energy of the sulfates decreases by

Answer 36

relatively smaller values

Question 37

The enthalpy change of hydration decreases by

Answer 37

relatively larger values down the group

Question 38

∆HꝊ sol becomes more

Answer 38

endothermic down the group

Question 39

Solubility of Group 2 sulfates decreases

Answer 39

down the group

Question 40

The higher the positive value of ∆HꝊ sol

Answer 40

he less soluble the salt

Question 41

Answer 41

Question 42

Entropy

Answer 42

a measure of the ‘disorder’ of a system, and that a system becomes more stable when its energy is spread out in a more disordered state

Question 43

Standard molar entropy is

Answer 43

the entropy when one mole of substance in its standard state

Question 44

The values of all molar entropies are

Answer 44

positive

Question 45

Gases generally have much

Answer 45

higher entropy values than liquids – which have higher entropy values than solids; hence the more gas molecules present, the greater the number of ways of arranging them, hence higher entropy:

Question 46

Answer 46

Increase in entropy of the system due to the greater number of moles of gas molecules in the products (5 molecules) than in the reactants (2 molecules); there are two different product molecules and only one type of reactant molecule, contributing to a greater disorder, increasing the stability (energetically) of the system

Question 47

Answer 47

 Decrease in entropy, hence the reactants are more stable than the product  Simpler substances with fewer atoms have lower entropy values than more complex substances (more no. of atoms)  For similar substances, the harder substance has lower entropy value  Gradual increase in entropy as the temperature of the substance is increased

Question 48

highest to lowest entropy

Answer 48

g>l>s

Question 49

For an exothermic reaction, energy released to

Answer 49

the surroundings, and causes translation and rotation of molecules in the surroundings – increasing its arrangements – hence there is likely to be an increase in entropy and increase in the chance for chemical change to occur spontaneously

Question 50

For an endothermic reaction, energy absorbed from

Answer 50

the surroundings, decreasing its arrangements, hence there is likely to be a decrease in entropy and decrease in the chance for a chemical reaction to occur spontaneously

Question 51

When the total enthalpy change is positive,

Answer 51

the reaction will occur spontaneously, reaction is feasible

Question 52

When total enthalpy change is negative,

Answer 52

he reaction is not likely to occur (not feasible)

Question 53

entropy formula

Answer 53

Question 54

Entropy change of the surroundings is given by:

Answer 54

Question 55

total enthalpy change formula

Answer 55

Question 56

During exothermic reactions

Answer 56

the enthalpy change plays a bigger role than the entropy change of the system

Question 57

kJmol-1 to JKmol-1

Answer 57

*1000

Question 58

gibbs free energy formula

Answer 58

Question 59

An exothermic reaction causes ∆Hreaction to be negative

Answer 59

 If the value of ∆Ssystem is positive, the reaction will be spontaneous, ∆G is negative  If the value of ∆Ssystem is negative in low temperatures, ∆G is negative  If the value of ∆Ssystem is negative in high, ∆G is positive

Question 60

An endothermic reaction causes ∆Hreaction to be positive

Answer 60

 If the value of ∆Ssystem is negative, ∆G is positive  If the value of ∆Ssystem is positive in high temperatures, ∆G is negative  If the value of ∆Ssystem is positive in low temperatures, ∆G is positive

Question 61

The electron affinity is a measure of the

Answer 61

attraction between the incoming electron and the nucleus - the stronger the attraction, the more energy is released – hence electron affinity increases upward for the groups and from left to right across periods of a periodic table