• A disturbance to a system at equilibrium causes Q to differ from K
• The reaction will “shift” to bring Q back into agreement with K

Effects of Changes to a System

• You can change the position of equilibrium, but not the actual value of equilibrium (K)
1. Pressure (only affects gasses); there are three ways to change the pressure of a system with gas

a. Effect of changing Pressure:

○ Increase pressure, the equilibrium will shift to the side with less moles of gas

○ Pressure decreases, equilibrium will shift to side to side with more moles of gas

b. Addition of an inert (unreactive) gas:

○ Increases the total pressure but has no effect on the equilibrium of the system or the concentrations or partial pressures of the reactants or products

c. Effect of changing Volume:

○ Increase volume: shift to side with more moles of gas

○ Decrease volume: shift to side with less moles of gas

1. Temperature: K will change depending on temp (treat energy as either a reactant or product)
• Ex: Endothermic

○ Treat heat as reactant

○ Effect on K: Adding heat will shift in forward direction so K > 1

○ Forward direction → high temp & LP; Reverse direction → low temp & HP

• Ex: Exothermic:

○ Treat heat as a product

○ Effect on K: Adding heat will shift in reverse reaction so K < 1

○ Forward direction → low temp & HP; Reverse direction → high temp and LP

1. Concentration: the system will shift away from the added component (or toward the removed component)
• If question adds something to system, it will likely react with smthn in the reaction

○ If add something that forms a precipitate (often OH-) → are taking reactant out of reaction

• What if dilute the solution? (ex: add water vapor)

○ Dilute → all molarities (products and reactants) will decrease

○ Diluting will always cause a shift toward more aqueous species

■ If there are more reactants (denominator) than products → Q > K

■ If there are more products (numerator) than reactants → Q < K

• What if increase the concentration of the solution?

○ Concentrate → all molarities (products and reactants) will increase

○ Concentrating will always cause a shift toward less aqueous species!

■ If there are more reactants (denominator) than products → Q < K

■ If there are more products (numerator) than reactants → Q > K

• Changing the amount of liquid/solid or adding a catalyst will have NO SHIFT