# What are "lattice" and "hydration energies"?

Dec 17, 2016

Well, $\text{lattice enthalpy is...................}$

#### Explanation:

Well, $\text{lattice enthalpy is the enthalpy associated with the }$
$\text{formation of one mole of an ionic solid from equiv quantites}$
$\text{of its constituent ions, with the reactant specified to be in the}$
$\text{gas phase.}$

And thus, for the lattice enthalpy of $\text{sodium chloride}$ we would interrogate the thermodynamics of the reaction:

$N {a}^{+} \left(g\right) + C {l}^{-} \left(g\right) \rightarrow N a C l \left(s\right) + \Delta$,

where $\Delta \equiv \text{Lattice enthalpy.}$

And while this is a hard measurement to make experimentally, there are enuff good thermodynamic data to allow the measurement by data from known experiments.

And $\text{hydration enthalpy}$ is the $\text{enthalpy associated with the}$
$\text{formation of one mole of hydrated ions from one mole of}$
$\text{gaseous ions that undergo hydration to give aquated ions.}$

${M}^{+} \left(g\right) + \text{excess water} \rightarrow {M}^{+} \left(a q\right) + \Delta$

Again, the data are good enuff to allow recourse to tabulated measurements.