Further energetics

Question 1

Define lattice enthalpy

Answer 1

The enthalpy change measured when one mole of an ionic solid is formed from its gaseous ions

Question 2

Define ‘standard enthalpy change of atomisation’

Answer 2

The enthalpy change measured when one mole of gaseous atoms are formed from an element in its standard state

Question 3

Define first electron affinity

Answer 3

The energy measured when one mole of atoms in the gaseous state gain an electron to form gaseous -1 ions

Question 4

Define second electron affinity

Answer 4

The energy measured when one mole of 1-charged atoms in the gaseous state gain an electron to form 2- ions

Question 5

Define first ionisation energy

Answer 5

Energy measured when 1 mole of gaseous atoms lose an electron to produce 1 mole of gaseous ions with a +1 charge

Question 6

Define second ionisation energy

Answer 6

Energy measured when 1 mole of gaseous atoms with a +1 charge lose an electron to produce 1 mole of gaseous ions with a +2 charge

Question 7

is formation of bond an endothermic or exothermic reaction and explain why?

Answer 7

exothermic reaction as energy is released when bonds are formed in order for them to be more stable

Question 8

Is breaking of bonds an endothermic or exothermic reaction?

Answer 8

Endothermic reaction as energy is required to overcome any inter-molecular forces holding them together

Question 9

Why are ionisation energy reactions;

-endothermic or exothermic

Answer 9

Endothermic as energy is required to overcome the electrostatic forces of attraction between the nucleus and electron on the furthermost shell

Question 10

Why is the second ionisation energy higher than the first ionisation energy

Answer 10

As it requires more energy to overcome the electrostatic forces between the positive nucleus and outermost electron.

Question 11

Describes differences between the first and second electron affinity reactions

Answer 11

First electron affinity = Exothermic
No energy needed to add electron to atom due to electrostatic forces of attraction between positive nucleus of neutral atom and negative electron, only energy released when the two bond together

Second electron affinity = Endothermic
Energy needed to overcome repulsion between negatively charged ion and electron. Energy needed to do this is greater than that released when bond is made

Question 12

What do we use the Born Haber Cycle for

Answer 12

To measure the lattice enthalpy of a solid ionic compound from its gaseous ions as its not possible to do such experimentally.

Question 13

In a Born Haber Cycle what does the direction of the arrow represent

Answer 13

Whether the specific reaction is endothermic or exothermic
(endothermic = Arrow going up)
(exothermic = Arrow going down)

Question 14

What can lattice energies be used to do and how?

Answer 14

Compare ionic bond strengths as the more negative it is then the stronger the ionic bond

Question 15

Are lattice energies endothermic or exothermic, explain why?

Answer 15

ALWAYS EXOTHERMIC, because bonds are formed not broken

Question 16

explain the effect of ionic charge and radius on the magnitude of the lattice energy of an ionic compound

Answer 16

• larger charge = greater forces of electrostatic attraction between ions
• smaller ions/ionic radius = smaller inter-ionic distance(ions sit closer together) = greater forces of attraction between oppositely charged ions

Question 17

what does a low lattice enthalpy tell us about an ionic compound

Answer 17

weak ionic bonds and that lattice is less endothermic

Question 18

What is the ionic model

Answer 18

The idea that all ions are spherical and have their charge evenly distributed

Question 19

Which is more accurate/reliable and why

experimentally or theoretically determined lattice enthalpy’s?

Answer 19

experimentally determined lattice enthalpy’s as they use experimentally determined enthalpy values to calculate it
whereas theoretically determines values using an equation and assuming that all ions ans spherical and distribute their charge evenly,which is not necessarily the case.

Question 20

The closer the theoretical and experimental value,what does this tell us?

Answer 20

That the ionic model is good for model for that compound

Question 21

The further away the theoretical and experimental value,what does this tell us?

Answer 21

That the ionic model isn’t so good for the model and needs to be modified, also tells us that there is some covalent character in the compound which resulted in the more negative experimental value

Question 22

What does comparing the theoretical and experimental value of a compound tell us?

Answer 22

The extent to which a compound resembles the purely ionic model

Question 23

What factors cause high covalent character in a molecule?

Answer 23

Cation with high polarising power

Anion that can be easily polarised

Question 24

What causes covalent character in ionic compounds?

Answer 24

Polarisation (cation polarising anion) as this causes a shift in the electron density from anion towards the cation, the sharing of electron density between two ions causes it to have some covalent character

Question 25

What does a cation need to have large polarising power - and how do these properties aid it.

Answer 25

(large charge density ) - attracts electrons towards itself more easily (positive nucleus)

• high charge
• small radius

Question 26

What does an anion need to be easily polarised - and how do these properties aid it.

Answer 26

High charge - More electrons to be polarised

large radius- electrons further away from nucleus - more shielding - easier for electrons to be attracted to cation

Question 27

What is so special about silver and zinc compounds

Answer 27

As they both have their outer electrons in the D orbital, electrons are more spaced out around orbital, so they have less shielding so are more easily distorted