Chapter x - Thermodynamics

Question 1

What is lattice dissociation enthalpy ΔL Hd?

Answer 1

Enthalpy change when one mole of an ionic crystal lattice is broken down into its constituent ions in their gaseous states

Question 2

What is lattice formation enthalpy ΔL Hf?

Answer 2

Enthalpy change when one mole of an ionic crystal lattice is formed from its constituent ions in their gaseous states

Question 3

What is an example equation for lattice dissocation enthalpy?

Answer 3

NaCl (s) –> Na+ (g) + Cl- (g)

Question 4

What is an example equation for lattice formation enthalpy?

Answer 4

Na+ (g) + Cl- (g) –> NaCl (s)

Question 5

What is enthalpy of formation?

Answer 5

Enthalpy change on forming one mole of a substance from its elements in their standard states under standard conditions, 298K, 100 kPa

Question 6

What is an example equation for enthalpy of formation?

Answer 6

Na (s) + 0.5 Cl2 (g) –> NaCl (s)

Question 7

What is first ionisation energy Δi H1?

Answer 7

Enthalpy change when one mole of gaseous atoms loses one mole of electrons to form one mole of gaseous monopositive ions

Question 8

What is an example equation for first ionisation energy?

Answer 8

Na (g) –> Na+ (g) + e-

Question 9

What is second ionisation energy Δi H2?

Answer 9

Enthalpy change when one mole of gaseous monopositive ions loses one mole of electrons to form one mole of gaseous dipositive ions

Question 10

What is an example equation for second ionisation energy?

Answer 10

Na+ (g) –> Na 2+ (g) + e-

Question 11

What is enthalpy of atomisation Δat H?

Answer 11

Enthalpy change when one mole of gaseous atoms are made from its element in standard states under standard conditions

Question 12

What are some example equations for enthalpy of atomisation?

Answer 12

Na (s) –> Na (g)
0.5 Cl2 (g) –> Cl (g)

Question 13

What is bond enthalpy/ bond dissociation energy?

Answer 13

Energy required to break one mole of a specified covalent bond, all substances in their gaseous states

Question 14

What is an example equation for bond enthalpy?

Answer 14

Cl2 (g) –> 2Cl (g)

Question 15

What is electron affinity Δea H/ EA?

Answer 15

Enthalpy change when mole of electrons is added to one mole of gaseous atoms to make one mole of gaseous mononegative ions

Question 16

What is an example equation for electron affinity?

Answer 16

Cl (g) + e- –> Cl- (g)

Question 17

What is a Born-Haber cycle?

Answer 17

A cycle that applies Hess’s Law used to calculate lattice enthalpy of an ionic compound

Question 18

What is enthalpy of solution ΔsolH?

Answer 18

Enthalpy change when one mole of an ionic substance dissolves in water under standard conditions to give a solution of infinite dilution

Question 19

What is enthalpy of hydration ΔhydH?

Answer 19

Enthalpy change when one mole of gaseous ions dissolve in sufficient water to give a solution of infinite dilution

Question 20

What is an example equation for enthalpy of solution?

Answer 20

NaCl (s) –> Na+ (aq) + Cl- (aq)

Question 21

What is an example equation for enthalpy of hydration?

Answer 21

Na+ (g) –> Na+ (aq)
Cl- (g) –> Cl- (aq)

Question 22

Why are there discrepancies between experimental and theoretical lattice enthalpies?

Answer 22

Theoretical lattice enthalpies assume that bonding in lattice is purely ionic meaning ions are perfectly spherical and have no covalent character
In reality, lots of ionic bonds have some covalent character, meaning the bonds are stronger so |ΔH|is greater.

Question 23

What is entropy and what are its units?

Answer 23

A measure of disorder of a system. Everything has some disorder so S is always greater than 0.
Units are J/Kmol

Question 24

What is change in entropy?

Answer 24

ΔS is the change in entropy for a reaction and can be negative.

Question 25

How does the entropy of different states compare?

Answer 25

Solid have lowest entropy and gases have highest entropy as disorder increases

Question 26

How does ΔS vap compare to ΔS fus?

Answer 26

ΔS vap is a lot greater as gases are a lot more disordered compare to liquids than liquids are to solids

Question 27

How is ΔS for a reaction calculated?

Answer 27

ΔS = ΣS products - ΣS reactants

Question 28

What is Gibbs Free Energy?

Answer 28

A measure of the feasibility of a chemical reaction

Question 29

What is the equation for Gibbs Free Energy?

Answer 29

ΔG = ΔH - TΔS
ΔG: gibbs free energy / kJ/mol
ΔH: enthalpy change / kJ/mol
T: temp/ K
ΔS: entropy change/ J/Kmol

Question 30

What is important to remember when using ΔS for Gibbs Free Energy equation?

Answer 30

ΔS is given in J/Kmol but needs to be converted to kJ/Kmol

Question 31

When is a reaction feasible?

Answer 31

When ΔG is less than or equal to 0, becomes feasible at the temperature where ΔG= 0