Steps in solving equilibrium problems:
1. List major species and concentrations based on information
given.
2. Brainstorm for reactions involving major species. Categorize
reactions as
(K<1),
(K>1) , or
(K so large it may not even be known; reaction goes to
completion).
3. Assume all
and
reactions go to completion.
Calculate new concentrations based on stoichiometry, and revise the
major species list accordingly. Return to step 2, changing all
formerly
reactions to
reactions (the reverse reaction).
4. When you are left with only
reactions in your list, brainstorm for other
or
reactions
involving minor products. Any
reaction followed by a
reaction
should be rewritten as a combination reaction (cf. solubility
equilibrium involving complexation).
5. List the K's and pick the dominant equilibrium, which usually
is the one with the largest K. Solve for x, the extent of this
equilibrium reaction.
6. Progress down the list of reactions from highest to lowest K,
using concentrations from previous reactions in further calculations.
Sometimes this approximation is not valid, and you must solve
simultaneous equations.