3.1.8 Thermodynamics Flashcards
Enthalpy of lattice formation definition
The standard enthalpy change when one mole of solid ionic crystal lattice is formed from its gaseous ions.
Enthalpy of lattice dissociation definition
The enthalpy change accompanying the breaking of one mole of an ionic solid into its constituent gaseous ions.
Enthalpy of formation definition
The enthalpy change accompanying the formation of one mole of compound from its constituent elements under standard states and conditions
Enthalpy of atomisation definition
The standard enthalpy change when one mole of gaseous atoms is formed from the element under its standard states and conditions
Ionisation energy definition
The energy required to remove one mole electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions
Bond enthalpy definition
The amount of energy required to break one mole of a specific covalent bond in one mole of gaseous compound
Electron affinity definition
The enthalpy change when mole of electrons is gained by one mole of gaseous atoms to form one mole og gaseous 1- ions
Explain evidence for covalent character from born-haber cycles
Lattice enthalpies from Born-Haber cycles are sometimes higher than the values calculated from assumptions based on the perfect ionic model. This is because many ionic compounds are not purely ionic but show some covalent character.
Enthalpy of hydration definition
the enthalpy change when one mole of gaseous ions is dissolved in water to give one mole of aqueous ions and a solution of infinite dilution
Gibbs-free energy equation
∆G = ∆H - T ∆S
∆H - change in enthalpy
∆S - change in entropy
T - temperature (K)
What values from the gibbs-free energy equation give feasible values
0 or negative values
-ve ∆H AND +ve ∆S
Always feasible
-ve ∆H AND -ve ∆S
Only feasible at lower temperatures
+ve ∆H AND +ve ∆S
Only feasible at higher temperatures
+ve ∆H AND -ve ∆S
Never feasible
Entropy definition
The measure of the level of disorder
Do feasible processes require extra energy after the initial
No
Things that increase entropy
Gaseous states
More moles
What do non-feasible processes need
A constant energy supply
Perfect order
0 kelvin where no particles have any kinetic energy
Enthalpy of solution definition
The enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution.
The enthalpy of hydration of Ca2+(g) is less exothermic than that of Mg2+(g), suggest why
M1 Ca2+ (ion) bigger than Mg2+
M2 weaker attraction to Oδ in water
What does enthalpy of solution equal
Enthalpy of lattice dissociation + Enthalpies of hydration
Explain why the second electron affinity of oxygen has a positive value
O- repels the electrons being added
