According to Le Chatelier's Principle what will happen to this equilibrium: C2H4O (g) ---> CH4 (g) + CO (g) if we decrease the size of the container?
The position of equilibrium will shift to the left and form more C₂H₄O.
Le Châtelier's Principle states that if you apply a stress to a system at equilibrium, the equilibrium will shift in the direction that will remove the stress.
The chemical equation for your equilibrium is
C₂H₄O(g) ⇌ CH₄(g) +CO(g)
If you decrease the size of the container, there will be too many molecules in the new volume.
The system will try to relieve the stress by decreasing the number of molecules.
If the reaction goes in reverse, two molecules convert into one molecule.
This relieves the stress, so the position of equilibrium will shift to the left, and more C₂H₄O will form.