NCEA Level 3 Chemistry – Aqueous Chemistry (AS91393) Practice Exam

Increasing pressure in a gas reaction influences the equilibrium position according to Le Chatelier's principle, which states that if a system at equilibrium is subjected to a change in pressure, the system will shift in the direction that counteracts that change.

In a reaction involving gases, if there is an uneven number of moles of gas on each side, an increase in pressure will favor the side that has fewer moles of gas. This is because, under higher pressure, the system will try to reduce the overall amount of gas present to relieve the stress of increased pressure. By shifting towards the side with fewer moles, it effectively decreases the total volume of gas, thereby lowering the pressure.

In contrast, if the reaction has the same number of moles on both sides or if one side has more moles, increasing pressure would not cause a shift since both sides would experience the same change. Therefore, in scenarios where there is an imbalance in the number of moles of gas, the correct outcome of increased pressure is a shift toward the side with fewer moles.