Studied by 0 peopleWhat two enthalpy changes occur when a solid ionic lattice dissolves in water?
Lattice enthalpy of dissociation (bonds between ions break to give (g) ions)
Enthalpy change of hydration (bonds between ions and water form)
Is lattice dissociation enthalpy endo/exo?
Endothermic.
Is the enthalpy change of hydration endo/exo?
Exothermic.
Why can water form bonds with the dissolving ions?
Water is a polar molecule. Positive ions form a weak bond with the delta negative oxygen and negative ions form a weak bond with the delta positive hydrogen.
How can enthalpy of solution be calculated?
Draw a Hess’ Law cycle.
Enthalpy change of solution goes on top, connecting solid ionic lattice and aqueous ions.
Lattice dissociation enthalpy is a downwards arrow on the bottom left connecting solid lattice to gaseous ions.
Enthalpies of hydration are upwards ions connecting gaseous ions to aqueous ions.
What is the direct route on a solution enthalpy Hess’ Law cycle?
Solid ionic lattice → aqueous ions (enthalpy of solution).
What is the indirect route on a solution enthalpy Hess’ Law cycle?
Solid ionic lattice → gaseous ions → aqueous ions
(lattice dissociation enthalpy + enthalpies of hydration)
How can you remember which enthalpy change is on top of a Hess’ Law cycle?
Enthalpy of SOLution → sol = sun so sol goes on top.
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