Final answer:
In gas-phase equilibrium systems with an equal number of moles on both sides of the reaction, a change in volume or pressure does not shift the equilibrium position. This is due to the equal molar volumes that gases occupy. When the number of moles on both sides is unequal, a volume or pressure change will favor the direction that re-establishes equilibrium by shifting toward fewer or more moles of gas, respectively.
Step-by-step explanation:
Effect of Volume and Pressure Changes on Equilibrium
When studying equilibrium systems, Le Chatelier's principle helps us understand how the system reacts to changes in conditions. Specifically, in a gas-phase equilibrium, the effect of a change in volume or pressure depends on the stoichiometry of the reaction. If an equilibrium system involves gases with an equal number of moles on the reactant and product sides, a change in volume or pressure will not affect the position of the equilibrium. This is because, according to Avogadro's law, equal numbers of moles of gases will occupy the same volume under the same conditions of temperature and pressure. Therefore, changes in pressure or volume do not provide any direction for the equilibrium to shift if the molar amounts of gas are the same.
However, when the number of moles of gases is different for reactants and products, a change in volume or pressure will result in a shift in equilibrium. An increase in pressure, or a decrease in volume, will favor the side of the reaction with fewer moles of gas, while a decrease in pressure, or an increase in volume, will favor the side with more moles of gas. These shifts occur as the system seeks to counteract the applied stress and re-establish equilibrium conditions.
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