In a decomposition reaction involving a gaseous product, what must be done for the reaction to reach equilibrium?

Decomposition reaction involving a gaseous product must be done in a closed vessel so that the gaseous products cannot escape from the reaction medium.

A reaction will reach equilibrium only when all the reactants and product will remain in the reaction medium. For this reason, decomposition reaction involving a gaseous product must be done in a closed vessel so that the gaseous products cannot escape from the reaction medium.

Now, for an example; decomposition of calcium carbonate

$CaC{O}_3\left(s\right)\stackrel{∆}{\to }CaO\left(s\right)+C{O}_2\left(g\right)$

In an open container, the product carbon dioxide will escape; hence the reaction only goes to the forward direction.

But in a closed container, the product carbon dioxide will not escape; hence, the reaction will perform the backward reaction as well. Therefore, the reaction will reach the equilibrium like

$CaC{O}_3\left(s\right)\stackrel{∆}{\rightleftarrows }CaO\left(s\right)+C{O}_2\left(g\right)$

Decomposition reaction involving a gaseous product must be done in a closed vessel so that the gaseous products cannot escape from the reaction medium and the backward reaction occurs as well. Therefore, the reaction can reach the equilibrium.