Thermodynamics

Question 1

Lattice enthalpy of formation

Answer 1

Enthalpy change when 1 mole of a solid ionic lattice is formed from its gaseous ions.

Question 2

Lattice enthalpy of dissociation

Answer 2

Enthalpy change when one mole of a solid ionic lattice separates into its gaseous ions

Question 3

Enthalpy of atomisation

Answer 3

Enthalpy change when one mole of gaseous atoms is formed from its element in its standard state

Question 4

Ionisation energy

Answer 4

Enthalpy required to remove one mole of electrons from one mole of gaseous atoms

Question 5

Electron affinity

Answer 5

Enthalpy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of negative ions

Question 6

Standard enthalpy of formation

Answer 6

Enthalpy change to form one mole of a substance, from its elements, in their standard state at 100kPa and 298K

Question 7

What is entropy?

Answer 7

A measure of disorder

Question 8

Which state has the most disorder?

Answer 8

Gaseous state

Question 9

How do you work out ΔS of a system?

Answer 9

ΣS products - ΣS reactants

Question 10

What is entropy when temp = 0K?

Answer 10

Zero

Question 11

When is their perfect order?

Answer 11

At absolute zero, as a crystal will have zero entropy

Question 12

What equation helps determine the feasibility of a reaction?

Answer 12

ΔG = ΔH - TΔS

Question 13

What does ΔG need to be in order for a reaction to be feasible?

Answer 13

ΔG < 0 (or =0)

Question 14

Scenario 1:

Is a reaction feasible with a negative ΔH and positive ΔS?

Answer 14

Yes, ΔG must be negative, so the reaction is completely feasible at all temperatures

Question 15

Scenario 2:

Is a reaction feasible with a positive ΔH and a positive ΔS?

Answer 15

ΔG is only negative if ΔH < TΔS. Reaction will just become feasible when ΔH = TΔS

Question 16

Scenario 3:

Is a reaction feasible with a positive ΔH and negative ΔS?

Answer 16

No, ΔG must be positive so the reaction is not feasible at any temperatures

Question 17

Scenario 4:

Is a reaction feasible with a negative ΔH and a negative ΔS?

Answer 17

ΔG is only negative if ΔH > TΔS (numerically). Reaction will just become feasible when ΔH = TΔS.

Question 18

Enthalpy of solution

Answer 18

Enthalpy change when one mole of a solid ionic compound completely dissolves into its aqueous ions

Question 19

Hydration enthalpy

Answer 19

Enthalpy change when one mole of gaseous ions completely dissolves in water

Question 20

How do you calculate enthalpy of solution?

Answer 20

Lattice enthalpy of dissociation + Hydration enthalpies

Question 21

What assumptions are made in born-haber?

Answer 21

• Perfect ionic model
• Perfect sphere
• No point charges
• No covalent character