5D - Lattice enthalpy & Free energy definitions

Question 1

Lattice enthalpy (Δ_LEH^⦵)

Answer 1

The enthalpy change where 1 mole of an ionic compound is formed from its gaseous ions under standard conditions

Question 2

Standard enthalpy change of formation (Δ_fH^⦵)

Answer 2

Enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states under standard conditions

Question 3

First ionisation energy (Δ_IE1H^⦵)

The 1 = 1st ionisation energy, it would 2 if it’s 2nd ionisation etc…

Answer 3

The enthalpy change when 1 mole of a electrons are removed from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

Question 4

Standard enthalpy change of atomisation (Δ_atH^⦵)

Answer 4

Enthalpy change when 1 mole of gaseous atoms are formed from their elements in their standard states under standard conditions

Question 5

1^st electron affinity (Δ_EA1H^⦵)

Don’t forget the circle with the line through it at the top of the H

The 1 will change on which electron affinity it is e.g. Δ_EA2H^⦵ would be 2^nd electron affinity

Answer 5

Enthalpy change when 1 mole of gaseous atoms gain 1 mole of electrons to form 1 mole of gaseous 1- ions

Question 6

The way you construct a Born-Haber cycle and the hess cycle that goes with it

Answer 6

Always do one thing after the other

Question 7

Hess cycle between Δ_rH^⦵, Δ_fH^⦵ and Δ_LEH^⦵

Answer 7

Question 8

Enthalpy (H)

Answer 8

The heat content stored in a chemical system

Question 9

Standard enthaply change of hydration (Δ_hydH^⦵)

Answer 9

The enthalpy change when 1 mole of gaseous ions are added to water to form 1 mole of aqueous ions under standard conditions

Question 10

Standard enthalpy change of solution (Δ_solH^⦵)

Answer 10

The enthalpy change when 1 mole of a ionic solid is completely dissolved in water under standard conditions

Question 11

Standard enthalpy change of neutralisation (Δ_neutH^⦵)

Answer 11

Enthalpy change of an acid/ base reaction to form 1 mole of water under standard conditions with reactants and products in their standard states

Question 12

Hess cycle linking Δ_solH^⦵ and Δ_hydH^⦵ together and explain the difference in the 2 routes

Answer 12

Route 1:

• Single step process of Δ_solH^⦵

Route 2:

• 2 step process
  
  • Ionic lattice is first broken down into constituent gaseous ions - inverse of Δ_LEH^⦵
  • During 2^nd step, ions become surrounded by, and form electrostatic interactions with solvent molecules. When solvent is H₂O this is referred to as Δ_hydH^⦵

Question 13

• Draw a born Haber type diagram to represent the Hess cycle linking Δ_solH^⦵ and Δ_hydH^⦵
• What is different about this digram compared to other born haber cycle diagrams?

Answer 13

• The arrow for Δ_solH^⦵ DOESN’T represent whether it’s endo/exothermic. It can be either but for this diagram it is always drawn facing upwards
• ∑Δ_hydH^⦵ represents the sum of all the individual enthalpy changes of hydration of the constituent gaseous ions

Question 14

Hess’s law

Answer 14

If a reaction can take place by more than 1 route and the initial and final conditions are the same, the total anthalpy change is the same for each route

Question 15

Standard conditions

Answer 15

Pressure = 100kPa / 1atm

Temperature = 298K / 25ºC

Concentration of solutions = 1moldm^-3

Standard physical states

Question 16

Entropy

Symbol and units = ?

Answer 16

Entropy = The degree of disorder in a system

Symbol = S

Units = JK^-1mol^-1

Question 17

Equation:

Entropy change = ?

Units = ?

Answer 17

Entropy change = ∑entropy change of products - ∑entropy change of reactants

ΔS = ∑S_products - ∑S_reactants

Units = JK^-1mol^-1

Question 18

Equation + definition:

Free energy

Units = ?

What the value of ΔG means for the reaction?

Answer 18

Free energy change (ΔG) = Measure of feasibility of a reaction

• ΔG < 0 (feasible)
• ΔG > 0 (not feasible)
• ΔG = 0 (boundary)

Units for Free energy (ΔG) = KJmol^-1

• ΔH = KJmol^-1 and ΔS = JK^-1mol^-1 ∴ remember to convert KJ → J by x1000!
• Temp must be in K

Question 19

ΔG = ΔH - TΔS

Explain how the value of ΔH and ΔS affect the value of ΔG.

HINT:

It’s the 2x2 grid!

Answer 19