Final answer:
Adding a catalyst to the reaction CO + H₂O → CO₂ + H₂ will not cause the equilibrium to shift in any direction. The catalyst will only increase the reaction rate, leaving the equilibrium concentrations unchanged.
Step-by-step explanation:
When adding a catalyst to the equilibrium reaction CO + H₂O → CO₂ + H₂, the equilibrium will not shift to either the left or the right. A catalyst only speeds up the reaction rate but does not affect the position of equilibrium. Therefore, the addition of a catalyst will have no effect on the equilibrium concentrations of the reactants and products. This principle is consistent across all reversible reactions, whether it involves gaseous components in the water-gas shift reaction or other phases in chemical reactions.