Carbon monoxide $(CO)$ reacts with hydrogen sulphide $(H_2S)$ at a constant temperature of $800\:K$ and a constant pressure of 2 bar as:
$$CO+H_2S\leftrightharpoons COS+H_2$$
The Gibbs free energy of the reaction ${\Delta g^\circ}_{rxn}=22972.3\:J/mol$ and universal gas constant $R=8.314\:J/(mol\:K).$ Both the reactants and products can be assumed to be ideal gases. If initially only $4\:mol$ of CO are present, the extent of the reaction (in mol) at equilibrium is _________ (rounded off to two decimal places).