Final answer:
Changing the pressure or volume of a system can shift the position of equilibrium in a gas-phase reaction but does not change the value of Keq, which remains constant unless the temperature changes.
Step-by-step explanation:
Does changing the pressure or volume of a system affect the Keq (equilibrium constant) of a reaction? The answer lies within the realm of chemical equilibrium and is governed by Le Chatelier’s principle. In essence, altering the pressure or volume of a gas-phase equilibrium system can cause a shift in the position of equilibrium but does not change the value of Keq itself.
When you increase the pressure of a system, by decreasing its volume, the equilibrium will shift to favor the formation of fewer moles of gas. This is because fewer moles of gas will occupy a smaller volume, thus reducing the imposed pressure increase. Conversely, if you decrease the pressure, by increasing the volume of the system, the equilibrium will shift to favor the side that produces more moles of gas, filling the increased volume.
It is crucial to observe that changes in total pressure, such as adding an inert gas, do not affect the partial pressures of the gases present in the equilibrium expression; therefore, they do not shift the equilibrium. The overall pressure or volume change effects are significant only when there is a change in the total number of moles of gas resulting from the reaction. In systems with equal moles of gas on both the reactants and products sides, changes in pressure and volume do not affect the equilibrium.
Le Chatelier’s principle is instrumental in predicting the direction of shift in response to volume and pressure changes. However, regardless of the shift, the equilibrium constant itself remains unchanged, indicating that Keq is solely dependent on the reaction conditions and not the concentration or pressure changes.