Energy

Question 1

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.

Question 2

ΔH FORMATION

Answer 2

When one mole of a compound is formed from its elements in their standard states under standard conditions
e.g. Cu(s) + ½O2(g) → CuO(s)

Question 3

ΔH Atomisation

Answer 3

When one mole of gaseous atoms is formed from the element in its standard state under standard conditions e.g. ½O2(g) → O(g)

Question 4

FIRST IONISATION ENERGY

Answer 4

When one electron is removed from each atom in one mole of gaseous atoms

Question 5

SECOND IONISATION ENERGY

Answer 5

When one electron is removed from each ion in one mole of gaseous 1+ ions

Question 6

FIRST ELECTRON AFFINITY

Answer 6

When one electron is gained by each atom in one mole of gaseous atoms (to form one mole of gaseous 1- ions)

Question 7

SECOND ELECTRON AFFINITY

Answer 7

When one electron is gained by each ion in one mole of gaseous 1- ions (to form one mole of gaseous 2- ions)

Question 8

Enthalpy change of solution

Answer 8

The enthalpy change that takes place when one mole of a compound is completely dissolved in water

Question 9

Enthalpy change of hydration

Answer 9

The enthalpy change for forming 1 mole of aqueous ions from 1 mole of gaseous ions

Question 10

What affects Lattice Enthalpy?

Answer 10

(i) ionic radius: there is a greater attraction between smaller ions and so lattice enthalpies become more negative as ionic radius decreases
(ii) ionic charge: there is a greater attraction between ions with higher charges and so lattice enthalpies become more negative as ionic charge increases.

Question 11

Processes take place when an ionic solid dissolves in water

Answer 11

(i) breakdown of the ionic lattice into gaseous ions (= reverse of the lattice enthalpy, requires energy)
(ii) hydration of the ions (releases energy, since bonds (ion-dipole attractions) are formed between the ions and water molecules)

Question 12

What affect ΔH Hydration?

Answer 12

(i) ionic radius
(ii) ionic charge
ΔH becomes more negative as ionic radius decreases and as ionic charge increases

Question 13

Define Entropy

Answer 13

A measure of the disorder of a system; a system becomes energetically more stable when it becomes more disordered

Question 14

Processes which Increase Entropy

Answer 14

(i) When a solid melts or a liquid boils. The gaseous state of a substance has a much higher entropy (much more disorder) than its liquid state, which in turn has a higher entropy than its solid state.
(ii) When a solid lattice dissolves: aqueous ions (usually) have more disorder than a solid lattice
(VERY rarely there an increase in order from (s) to (aq) – just be aware of it)
(iii) When there is an increase in the number of gaseous molecules

Question 15

How to calculate Entropy?

Answer 15

ΣSproducts - ΣSreactants

Question 16

Free Energy Change (ΔG)=

Answer 16

ΔH – TΔS

Question 17

Feasibility of Reaction when

ΔH is positive ΔS is positive

Answer 17

Reactions are only feasible ABOVE a certain temperature. i.e. works best at high temperatures

Question 18

Feasibility of Reaction when

ΔH is negative ΔS is positive

Answer 18

Feasible at all temperatures

Question 19

Feasibility of Reaction when

ΔH is positive ΔS is negative

Answer 19

Never feasible at any temperature

Question 20

Feasibility of Reaction when

ΔH is negative ΔS is negative

Answer 20

Reactions are only feasible BELOW a certain temperature. i.e. works best at low temperatures