1.6 - Thermodynamics

Define the Enthalpy of Formation

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

Define the Enthalpy of Atomisation of:

• Element

• Compound

Element:

• Enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state

Compound:

• Enthalpy change when 1 mole of compound in its standard state is converted into gaseous atoms

Define the Enthalpy of Ionisation

The enthalpy change when 1 mole of (higher charged) positvely charged gaseous ions are formed from 1 mole of gaseous atoms/ lower charged ions

Define the Electron Affinity

The enthalpy change when 1 mole of negatively charged gaseous ions are formed from 1 mole of gaseous atoms/lower charged ions

Define the Enthalpy change of Hydration:

• Is it Endo or Exo (+why)

• 2 factors (how)

The enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions:

• Always Exothermic as ion-dipole forces are being made (bond making = exo)

• 2 Factors:

  • Ion size = Larger = Lower charge density = Lower enthalpy of Hydration

  • Charge of ions = Larger = Higher charge density = Higher enthalpy of Hydration

Define the Enthalpy change of Solution

The enthalpy change when 1 mole of solute (ionic solid) is dissolved in enough solvent (water) such that no further enthalpy change occurs despite further dilution

Define the Enthalpy of Lattice Dissociation (exo or endo)

Enthalpy change when 1 mole of a solid ionic lattice is broken into 1 mole of its gaseous ions:

• ENDO

Define the Enthalpy of Lattice Formation (exo or endo)

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

• EXO

Why is the 1st electron affinity different to further affinities? 

• Include exo + endo in definition

Adding an electron is exothermic as attraction from the atoms nucleus is larger than electron repulsion - therefore since energy needed to remove electrons, energy is released to add an electron 

• EXO

Other affinities are adding additional electrons to -ve ions the repulsion>attraction energy is now needed to “absorb” the electrons 

• ENDO

What are Hydrated ions?

Ions formed when salt is dissolved in water and bond to polar water molecules

What 2 enthalpies determine a salts -ve/+ve enthalpy of solution? (how)

Enthalpy of lattice dissociation (endo) + Bond making of Ion dipole forces aka. Hydrated ions (exo):

• The sum of these 2 determine the salts overall sign and its enthalpy nature (endo or exo)

BORN HABER CYCLES USE CHEM NOTES 2

BORN HABER CYCLES USE CHEM NOTES 2

What is Entropy?

Measure of disorder in a system, the number of ways particles and their energy can be arranged

Rank the states of matter by entropy (LEAST → MOST)

1. Solid

2. Liquid

3. Gas

Give the formula for entropy change

ΔS.system = ΣS.products - ΣS.reactants

Give the Gibbs Free energy change formula

ΔG = ΔH - TΔS

How can you determine if a reaction is feasible (ΔG)

• ΔG < 0 (Negative): The reaction is feasible and likely to occur

• ΔG > 0 (Positive): The reaction is not feasible

• ΔG = 0: The reaction is at equilibrium, meaning it is just becoming feasible

How do you determine the minimum temperature when a reaction is feasible or not?

Set ΔG=0, then rearrange for T

List out the enthalpy, entropy, Gibbs free + feasibility table