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I know that the change in pressure doesn't effect the equilibrium constant. According to my lecture notes from week 1 Friday, Lavelle stated that when there is a change in pressure there is no effect on the reaction or in reactant and product concentrations. However if volume decreases, and there are more moles of gas on the left (reactant side) then the reaction will shift right (towards the product). But if the volume decreases and the are more moles of gas on the right (product side), then the reaction will shift to the left (reactant side).
Increasing pressure by decreasing the volume will cause a shift to the side with fewer moles of gas, and decreasing pressure by increasing volume causes a shift to the side with more moles of gas. If you change the pressure by adding an inert gas into the system, then nothing changes.
In order to determine how a change in pressure affects the equilibrium of a system, it must be said how the pressure was changed in the first place. As the above comments said, if the pressure is increased by adding an inert gas, there will be no change in equilibrium, since the partial pressures of the system remain unaffected. If the pressure is changed by changing the volume, you must calculate the new concentrations of the reactants and products, calculate Q, and compare it to K in order to see which way the reaction will shift. If the pressure is changed by increasing or decreasing the partial pressure of a reactant or product, the reaction will shift just as if you had increased or decreased the concentration of the same reactant or product. Hope this helps!
I had a similar question and I'm not sure if it's right, but when I looked it up, it said that increasing the pressure, the reaction will shift towards the side with fewer moles of gas. And just the opposite for a decrease in pressure.
It is important to note that PV=nRT only stands true if the increase in pressure changes concentration; adding an inert gas such as helium to the system will increase the pressure but make the volume remain the same, thus no change in K occurs.
if the pressure is changed without a change in volume (i.e. by adding an inert gas), then the reaction does not shift. If it is changed due to a volume change, then the reaction will favor the side with the fewest overall moles of gas.
Increasing the pressure will in turn decrease the volume of the container in which the specimens are contained: the side with less moles of gas favored as there are fewer molecules on that side of the reaction = smaller volume.
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