When volume is decreased (therefore pressure increases), the equilibrium shifts toward which side?

When volume is decreased (therefore pressure increases), the equilibrium shifts toward which side?

• A. Toward more gas molecules
• B. No change
• C. Toward non-gaseous species only
• D. Toward fewer gas molecules

Answer: (D)

When you decrease the volume, the pressure goes up, and the system responds to counter that change. In gaseous equilibria, it does this by reducing the total number of gas particles. So the equilibrium shifts toward the side with fewer gas molecules. If that side ends up being the products, you’d move in that direction; if it’s the reactants, you’d move there instead. The driving idea is to minimize the pressure by decreasing the amount of gas present, not toward more gas, not staying the same, and not exclusively toward non-gaseous species.

When you decrease the volume, the pressure goes up, and the system responds to counter that change. In gaseous equilibria, it does this by reducing the total number of gas particles. So the equilibrium shifts toward the side with fewer gas molecules. If that side ends up being the products, you’d move in that direction; if it’s the reactants, you’d move there instead. The driving idea is to minimize the pressure by decreasing the amount of gas present, not toward more gas, not staying the same, and not exclusively toward non-gaseous species.