AP Chem unit 7

When equilibrium is reached, there are no observable changes in the system: both reactants and products are present with constant concentrations/partial pressures. Forward and reverse processes occur at equal rates. Dynamic equilibrium is defined by the condition where the rate of the forward reaction equals that of the backward reaction.

• Q^c: relative concentrations of the reaction species

• Q^p: partial pressures

• K^c = Q^c

• K^p = Q^p

Q indicates the extent to which the reaction has proceeded:

• At equilibrium, Q = K

• Q > K: too many products, reaction shifts left

• K > Q: too many reactants, reaction shifts right

When reversing a reaction, K becomes the reciprocal of the forward K. If coefficients are multiplied, K is raised to that power.

Le Châtelier’s principle explains how the system responds to changes in chemical species concentrations, temperature, volume/pressure, or dilution:

• Increase in temperature shifts toward the endothermic direction

• Decrease in temperature shifts toward the exothermic direction

• Temperature change results in K change: right shift = K increase, left shift = K decrease

Ksp is the equilibrium constant for the dissolution of an ionic solid. If Qsp > Ksp, a precipitate forms. If Ksp > Qsp, no precipitate is formed.