Define enthalpy change of hydration (ΔH⦵hyd).
Enthalpy change of hydration is the enthalpy change that occurs when one mole of aqueous ions is formed from one mole of gaseous ions.
For example, the equation for the enthalpy change of hydration of Na is:
Na+(g) + aq ➔ Na+(aq).
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Define enthalpy change of solution (ΔH⦵sol).
Enthalpy change of solution is the enthalpy change that takes takes place when 1 mole of an ionic solid dissolves in sufficient water to form a very dilute solution.
For example, the equation for the enthalpy change of solution of NaCl is:
NaCl(s) ➔ NaCl(aq)
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What enthalpy changes do the arrows A-C represent?
ALattice enthalpy.
BEnthalpy of hydration.
CEnthalpy of solution.
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How can the solubility of a compound in water be predicted from its ΔH⦵sol value?
A compond is likely to be soluble in water only if ΔH⦵sol is negative or has a small positive value.
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State and explain the factors that lead to more exothermic values of ΔH⦵hyd?
The factors affecting ΔH⦵hyd values are:
This is beause ions with a larger charge and smaller radius can form stronger electrostatic attractions with polar water molecules.
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What is the equation that links enthalpy change of solution (ΔHsol), enthalpy change of hydration (ΔHhyd), and lattice enthalpy (ΔHlatt)?
ΔHsol = -ΔHlatt + ΔHhyd
This equation can also be written as ΔHsol = ΔHhyd - ΔHlatt
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