How is the attainment of equilibrium recognised in case of following equilibria?

Dissociation of magnesium carbonate in a closed vessel.

${\mathrm{K}}_{\mathrm{p}}$ for the following reaction will be equal to

$3{\mathrm{Fe}}_{\left(\mathrm{s}\right)}+4{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{g}\right)}\rightleftharpoons {\mathrm{Fe}}_3{\mathrm{O}}_{4\left(\mathrm{s}\right)}+4{\mathrm{H}}_{2\left(\mathrm{g}\right)}$

How is the attainment of equilibrium recognised in case of following equilibria?

Dissociation of ${\mathrm{N}}_2{\mathrm{O}}_5$ in a closed vessel.

Which of the following reaction involve homogeneous equilibrium and which involve heterogeneous equilibrium?

$2\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{s}\right)\stackrel{ }{\rightleftharpoons }2\mathrm{CuO}\left(\mathrm{s}\right)+4{\mathrm{NO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$