3.1.8 - Thermodynamics Flashcards
Define ‘enthalpy change’
Heat energy change at a constant pressure.
Define ‘standard enthalpy change’
Enthalpy change measured under standard conditions.
Define ‘enthalpy of atomisation’
Enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state.
Define ‘1st ionisation enthalpy’
The enthalpy change when 1 mole of gaseous 1+ ions is formed from its gaseous atoms.
Define ‘2nd ionisation enthalpy’
The enthalpy change when 1 mole of gaseous 2+ ions are formed from gaseous 1+ ions.
Define ‘1st electron affinity’
The enthalpy change when 1 mole of gaseous 1- ions are formed from gaseous atoms.
Define ‘2nd electron affinity’
The enthalpy change when 1 mole of gaseous 2- ions is formed from gaseous 1- ions.
Define ‘bond dissociation enthalpy’
The enthalpy change when 1 mole of covalent bonds is completely separated to form gaseous atoms.
Define ‘lattice enthalpy of formation’
The enthalpy change when 1 mole of solid ionic compound is formed from gaseous ions.
Define ‘lattice enthalpy of dissociation’
The enthalpy change when 1 mole of solid ionic compound dissociates into gaseous ions.
State 2 factors that form the perfect ionic model.
- Ions are perfect spheres. 2. With evenly distributed charge.
In what scenario is covalent character more likely for an ionic compound?
- Cation has high charge density. 2. Anion has low charge density.
How does covalent character change the lattice enthalpy?
Larger than expected as it requires more energy to break/form.
State the 2 factors that lattice enthalpy depend on and how.
- Size of ions (bigger size, charges are further apart, weaker attraction). 2. Charge on the ion (bigger charge, stronger attraction).
What are the 3 main factors that impact entropy?
- Physical State. 2. Dissolving. 3. Number of particles.
What is the formula for entropy?
ΔS = Σ S_prod - Σ S_react.
If ΔS is +ve, is a reaction likely? What if it’s endothermic?
It means a reaction is likely even if it’s endothermic.
Using ΔG, how can you tell if a reaction is feasible?
- If ΔG is -ve (or 0) the reaction is feasible. 2. If ΔG is +ve the reaction is not feasible.
Recall briefly how we use calorimetry to measure energy stores in sample.
- Dry sample weighed + burnt in pure oxygen. 2. In a sealed container. 3. Temperature increase of the fixed volume of water used to calculate energy released.
Define Enthalpy of formation
The enthalpy change when one mole of a compound is formed from its elements in its standard states under standard conditions.
Define Lattice enthalpy of formation
The enthalpy change when one mole of a solid ionic compound is formed from its gaseous ions under standard conditions.
In the Born-Haber cycle, what are up arrows?
Endothermic.
Endothermic is a
Positive enthalpy change.
Why would the lattice enthalpy be different from the theoretical value?
Doesn’t follow a perfectly ionic model and has some covalent characteristics in between.