Thermodynamics Flashcards
Lattice enthalpy of formation
Enthalpy change when 1 mole of a solid ionic lattice is formed from its gaseous ions.
Lattice enthalpy of dissociation
Enthalpy change when one mole of a solid ionic lattice separates into its gaseous ions
Enthalpy of atomisation
Enthalpy change when one mole of gaseous atoms is formed from its element in its standard state
Ionisation energy
Enthalpy required to remove one mole of electrons from one mole of gaseous atoms
Electron affinity
Enthalpy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of negative ions
Standard enthalpy of formation
Enthalpy change to form one mole of a substance, from its elements, in their standard state at 100kPa and 298K
What is entropy?
A measure of disorder
Which state has the most disorder?
Gaseous state
How do you work out ΔS of a system?
ΣS products - ΣS reactants
What is entropy when temp = 0K?
Zero
When is their perfect order?
At absolute zero, as a crystal will have zero entropy
What equation helps determine the feasibility of a reaction?
ΔG = ΔH - TΔS
What does ΔG need to be in order for a reaction to be feasible?
ΔG < 0 (or =0)
Scenario 1:
Is a reaction feasible with a negative ΔH and positive ΔS?
Yes, ΔG must be negative, so the reaction is completely feasible at all temperatures
Scenario 2:
Is a reaction feasible with a positive ΔH and a positive ΔS?
ΔG is only negative if ΔH < TΔS. Reaction will just become feasible when ΔH = TΔS
