# Would magnesium and calcium hydroxide undergo a single replacement reaction?

Can calcium hydroxide react with magnesium (if given sufficient activation energy) to produce magnesium hydroxide and calcium, in the same way that NaOH + $\ce{Mg} \ce{->} \ce{Mg(OH)2} + \ce{Na}$ ?

Or, is calcium's electronegativity (or some other factor) prohibitive of this?

The key part of the question is given sufficient energy. The difference in electronegativity between Ca and Mg is ~0.3 eV. The relationship of eV:K is about 1:12,000. Given that, you should be able to calculate a temperature at which the reaction $\ce{Ca(OH)2 + Mg -> Mg(OH)2 + Ca}$ is favored over the reverse.
Furthermore, you can force the suggested reaction by making use of relative solubilities. Find a solvent (not water, since magnesium and calcium are far more electronegative than hydrogen, and would decompose water to form hydroxides of both metals) in which $\ce{Ca(OH)2}$ is more soluble than $\ce{Mg(OH)2}$. Precipitation will "lock up" the $\ce{Mg(OH)2}$ as it forms, little by little, forcing the reaction to proceed even though it is endothermic.