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When a chemical system at equilibrium is disturbed by a change in a property (such as concentration, temperature or pressure), the system in a way that opposes the change.
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By increasing the pressure, we drive the reaction to the side where there are fewer total particles, or smaller concentration (forward in this case)
By decreasing the pressure, we drive the reaction to the side where there are more total particles or larger concentration (reverse in this case)
Note: Pressure only affects gases as you cannot change volume of a liquid (does not affect aqueous states).
Remember that P and V are related inversely
When volume is decreased (pressure increased), reaction shifts in favour of the side with fewer moles
In this case, reaction shifts right, favours forward reaction, products increase, reactants decrease
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