3.1.8 Thermodynamics Flashcards
Enthalpy of formation
EC when 1 mole of compound formed from elements in standard states and conditions
Lattice enthalpy
Energy change when 1 mole of a solid ionic compound formed from its gaseous ions under standard conditions
Enthalpy of combustion
Enthalpy change when one mole of a substance is burned completely in oxygen under standard conditions
Atomisation Enthalpy
The energy required for the formation of a mole of gaseous atoms under standard conditions.
Enthalpy of Electron Affinity
The enthalpy change when one mole of electrons is added to a mole of gaseous atoms under standard conditions
How 2 Born-Haber cycle?
∆H (enthalpy of formation) = Everything else added (diagram)
What are two things you should be careful of when doing Born-Haber cycles?
- The direction of the right hand arrow
- The step to turn 1/2O2 into O
Enthalpy of hydration
The enthalpy change when one mole of gaseous ions is dissolved in water to form one mole of aqueous ions under standard conditions
Entropy increases…
- With temperature
- Change in state
How do you calculate entropy of a reaction?
Entropy of products - entropy of reactants
Gibbs Free-Energy equation
∆H-(Tx∆S/1000)
When is a reaction feasible?
When ∆G>0
Why is the theoretical and experimental value of lattice enthalpy different?
- Compound may have partial covalent character
- Theoretical value assumes perfect ionic bonding
Why is the electron affinity value negative?
- Attraction between nucleus and electrons
- Causes energy to be released
Why is hydration exothermic?
- Water is polar
- So ion is attracted to hydrogen/oxygen in water
- Causing energy to be released
What should you be careful of when calculating bond enthalpy?
If it is 0.5 F2, then times the value you get by 2, as bond enthalpy is the enthalpy change when one mole of bonds is broken
