Chapter 22 Enthalpy And Entropy

Question 1

What is the enthalpy change of formation?

Answer 1

The enthalpy change that occurs when one mole of a compound is formed from its elements in their standard states under standard conditions

Question 2

What is the enthalpy change of combustion?

Answer 2

The enthalpy change that occurs when one mole of a substance is completely combusted in oxygen under standard conditions

Question 3

What is the enthalpy change of neutralisation?

Answer 3

The enthalpy change that occurs when one mole of water is formed during a neutralisation reaction between an acid and an alkali under standard conditions

Question 4

What is the enthalpy change of a reaction?

Answer 4

The enthalpy change when a chemical reaction occurs under standard conditions in the stoichiometric ratios of the balanced equation

Question 5

State whether the enthalpy change of formation is endothermic or exothermic

Answer 5

Exothermic

Question 6

What is enthalpy change of atomisation?

Answer 6

The enthalpy change that occurs when one mole of gaseous atoms are formed from its elements in their standard states

Question 7

State whether the enthalpy change of atomisation is endothermic or exothermic

Answer 7

Endothermic

Question 8

What is bond enthalpy?

Answer 8

The enthalpy change when one mole of a covalent bond is broken in the gaseous state

Question 9

State whether bond enthalpy is endothermic or exothermic

Answer 9

Endothermic

Question 10

What is first ionisation energy?

Answer 10

The enthalpy change that occurs when one mole of electrons are removed from one mole of gaseous atoms to produce one mole of gaseous +1 ions

Question 11

State whether first ionisation energy is endothermic or exothermic?

Answer 11

Endothermic

Question 12

What is second ionisation energy?

Answer 12

The enthalpy change that occurs when one mole of electrons are removed from one mole of gaseous +1 ions to produce one mole of gaseous 2+ ions

Question 13

State whether second ionisation energy is endothermic or exothermic

Answer 13

Endothermic

Question 14

What is first electron affinity?

Answer 14

The enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions

Question 15

State whether first electron affinity is endothermic or exothermic

Answer 15

Exothermic

Question 16

What is second electron affinity?

Answer 16

The enthalpy change that occurs when each ion in one mole of gaseous 1- ions gains one electron to form one mole of gaseous 2- ions

Question 17

State whether second electron affinity is endothermic or exothermic

Answer 17

Endothermic

Question 18

What is hydration enthalpy?

Answer 18

The enthalpy change when one mole of gaseous ions become hydrated (dissolved in water)

Question 19

What is enthalpy of solution?

Answer 19

The enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well separated and do not interact with each other.

Question 20

What is lattice enthalpy?

Answer 20

The enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gas phase

Question 21

State whether lattice enthalpy is endothermic or exothermic

Answer 21

Exothermic

Question 22

What factors can affect lattice enthalpies?

Answer 22

The greater the ionic charge the more exothermic the lattice enthalpy will be because there is a stronger attraction between ions

The smaller the ionic radius the more exothermic the lattice enthalpy because there is a stronger attraction between ions

Question 23

What is entropy?

Answer 23

A measure of the dispersal of energy
Also known as the measure of disorder

Question 24

How does entropy change with the level of disorder?

Answer 24

The higher level of disorder = the higher entropy
The lower level of disorder = the lower entropy

Question 25

How do entropy values change with the different physical states?

Answer 25

From solids —> liquids —> gases
Entropy increases because gases are more disordered

Question 26

What is the symbol used for entropy?

Answer 26

S

Question 27

What are the units of entropy?

Answer 27

JK-1mol-1

Question 28

How does entropy change with temperature?

Answer 28

As temperature increase entropy will also increase as the level of disorder increases

Question 29

Predict whether the entropy value will increase or decrease
LiCO3 (s) —> Li2O (s) + CO2 (g)

Answer 29

The entropy will increase because there is more disorder on the products side.
This is because Li2CO3 (s) forms Li2O (s) and CO2 (g) - there are two products formed including a gas which shows there will be a higher degree of disorder.

Question 30

Predict whether the entropy value will increase or decrease
SO2 (g) + 2H2S (g) —-> 3S (s) + 2H2O (g)

Answer 30

The entropy will decrease because there are 3 mole of gas on reactant and only 2 moles of gas on products alongside 3 moles of a solid showing that there is a higher degree of disorder on the reactants side.

Question 31

How is entropy calculated?

Answer 31

∆S = ∑(entropies of products) — ∑ (entropies of reactants)