22.3 Factors affecting Lattice Enthalpy + Hydration
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What factors affect lattice enthalpy?
IONIC RADIUS IONIC CHARGE
How does ionic radius affect lattice enthalpy?
￪ ionic radius ￬ ELECTROSTATIC ATTRACTION between oppositely charged ions in ionic lattice WEAKER ionic bonds less ENERGY RELEASED during formation of these bonds LESS EXOTHERMIC lattice enthalpy
What overall determines lattice enthalpy?
IONIC BOND STRENGTH
How does ionic charge affect lattice enthalpy?
￪ ionic charge ￪ ELECTROSTATIC ATTRACTION between oppositely charged ions in ionic lattice STRONGER ionic bonds more ENERGY RELEASED during formation of these bonds MORE EXOTHERMIC lattice enthalpy
What factors affect hydration enthalpy?
IONIC RADIUS IONIC CHARGE
What overall determines hydration enthalpy?
INTERMOLECULAR BOND STRENGTH between IONS + H2O
How does ionic radius affect hydration enthalpy?
￪ ionic radius WEAKER PERMANENT DIPOLE between IONS + H2O less ENERGY RELEASED during formation of these forces LESS EXOTHERMIC hydration enthalpy
How does ionic charge affect hydration enthalpy?
￪ ionic charge STRONGER PERMANENT DIPOLE between IONS + H2O more ENERGY RELEASED during formation of these forces MORE EXOTHERMIC hydration enthalpy
How can lattice enthalpy be an indicator of the melting point of an ionic compound?
lattice enthalpy = measure of bond strength MORE EXOTHERMIC LE = STRONGER ionic bonds, which require MORE ENERGY to break = HIGHER m.p
During changes of state of simple covalent molecules, intermolecular forces are overcome. However, giant ionic lattices have no intermolecular forces, ∴ become molten by…
breaking ionic bonds between oppositely charged ions
How can hydration enthalpy be a measure of intermolecular force (permanent dipoles) strength?
MORE EXOTHERMIC hyd = more ENERGY RELEASED during formation of permanent dipoles = stronger permanent dipoles
What type of intermolecular force is formed between dissociated gaseous ions of the ionic lattice + H2O molecules during hydration enthalpy?
permanent dipole
What is lattice enthalpy a measure of?
ionic bond strength
What is hydration enthalpy a measure of?
intermolecular force strength between dissociated ions + H2O molecules.
If lattice enthalpy is more exothermic, ionic bonds are ____.
stronger. ∵ more energy released during formation, so require more energy to break.
If lattice enthalpy is less exothermic, ionic bonds are ____.
weaker. ∵ less energy released during formation, so require less energy to break.
Which factors give a more exothermic lattice enthalpy?
(factors increasing electrostatic attraction between oppositely charged ions) smaller ionic radius + greater ionic charge
Which factors give a less exothermic lattice enthalpy?
(factors decreasing electrostatic attatraction between oppositely charged ions) larger ionic radius + lower ionic charge
Which factors give a more exothermic hydration enthalpy?
(factors increasing permanent dipole strength between ions + H2O) smaller ionic radius + greater ionic charge
Which factors give a less exothermic hydration enthalpy?
(factors decreasing dipole strength between ions + H2O) larger ionic radius + lower ionic charge
What should the enthalpy of solution be if a substance is soluble in water?
exothermic LE < Δhyd for both ions
what should the enthalpy of solution be if a substance is insoluble in water?
endothermic LE > Δhyd for both ions
What are ionic liquids?
ionic compounds which are liquid below 100°C
What are the properties of ionic liquids?
Conduct electricity Do not vaporise easily Dissolve wide range of substances