- 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)
- 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
- 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
- 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