When a chemical system at equilibrium is disturbed, the system shifts in a direction that minimizes the disturbance (the system will respond to relieve the stress and re-establish equilibrium).

 An increase in the concentration of a species will shift the equilibrium to the opposite side.  A decrease in concentration of a species will shift the equilibrium to the same side.

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 An increase in pressure will shift the equilibrium to the side with fewer gaseous molecules. Nature can reverse the pressure increase by decreasing the number of collisions.  A decrease in pressure will shift the equilibrium to the side with more gaseous molecules. Nature can reverse the pressure reduction by increasing the number of collisions.

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 Volume changes are interpreted as pressure changes from Boyle’s Law. Decreasing the volume will increase the pressure and increasing the volume will decrease the pressure.  Increasing the volume causes the reaction to shift in the direction that has more moles of gas particles  Decreasing the volume causes the reaction to shift in the direction that has fewer moles of gas particles

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 Endo Exo Endo Exo Endo Exo Endo

 Adding similar ions will shift equilibrium  Addition of a substance containing an ion that is common to the equilibrium system will increase the concentration of that ion, and the equilibrium will shift to reduce the concentration of that ion

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 Catalyst – a substance that increases the rate of a chemical reaction but is not consumed by the reaction  Catalysts lower the activation energy making it easier for reactants to get over the energy hump. Activation energy – amount of energy that must be absorbed by reactants before a reaction can occur; an energy hump that normally exists between the reactants and products. Activated Complex – point at which the reaction will go to completion or go back to reactants. Enthalpy ( Δ H) is the energy difference between the reactants and products  Exothermic reactions have a negative Δ H  Endothermic reactions have a positive Δ H

 A catalyst does not change the position of equilibrium; only how fast equilibrium is reached.  A catalyst does not change the value of K eq for a reaction; it affects only the rate of reaction