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<center>Equilibrium: Calculating Equilibrium Constant,K: (Knowing Equilibrium Info)</center>
 
Procedures for Calculating any Equilibrium Constant Problem 
 
Step 1 : Write down balanced chemical reaction 
Step 2 : Determine and write down the Equilibrium Constant Expression (K=<nowiki>[products]</nowiki>E/<nowiki>[reactant]</nowiki>E) where E = Equilibrium conditions. 
Step 3: Plug in and do math to solve for unknown. (3 Levels of Difficulty) 
Level 1 : Simplest Difficulty 
*Problems gives all equilibrium concentration and you are solving for K (would be nice to figure out units also). See example below.
*Problem gives all equilibrium concentrations except one and gives value of K (you need to determine units of K) and solving for last equilibrium concentration., ([http://www.tmcleod.org/Level1/Chem328KineticEquil/Chem328ExampleofWorkSimpleEquilibrium.pdf Example of Work for Simple Equilibrium Problems]. Remember, you need to manipulate the equation, in this case, equilibrium constant expression into a form with your unknown on one side of equal sign and all other variable on other side of equal sign.
 
Level 2 : ICE Box without "x" (have one piece of information at equilibrium) 
*[[Direction on Calculation ICE Box without "x" Problems]]
* For example of work, click here [http://www.tmcleod.org/Level1/Chem328KineticEquil/Chem328ExampleofWorkICEBox.pdf Example of Work for a Simple ICE Box (no x)]
 
Level 3 : ICE Box with "x" (will not do in 1st year, but will in AP Chem) 
##Sometimes they give all equilibrium concentrations and look for Equilibrium constant (K).
##Sometime they give K and you are looking for one of the species' equilibrium concentration (they give all other species' equilibrium concentrations)
##Sometimes they give concentration of one reactant and/or product at equilibrium and all other species' initial concentrations and you are calculating K.
**If this occurs, all you Wizards of Stoichiometry need to set-up <nowiki>ICE Box table</nowiki>.
**i. Change mole and container of initial conditions into concentration (Molarity, M).
**ii. Convert one piece of equilibrium to mole or M reacted.
**iii. Take M reacted and use stoichiometry to determine amount of all other species reacted or producted in rxn
**iv. Use math on table to determine equilibrium concentration of all species. 
 
Example 1 
Calculate the Equilibrium constant for the following reversible reaction @25o: 
2 NO(g) + 1 O2 (g) <==> 2 NO2 (g) 
where the equilibrium concentration of NO,O2,and NO2 are 2.00M,4.00M,and 3.00M, respectively. 
Answer: 
Step 1: Balanced chemical reaction. See question 
Step 2: Write down Equilibrium constant expression: 
K= {NO2 (g)}2 / {O2 (g)}1{NO(g)}2 
But write it like this : 
 
Step 3: plug in known information into Equilibrium constant expression directly since you know all equilibrium concentration. 
K = (3.00M)2 / {(2.00M)2)(4.00M)1} 
K=0.5625 = 0.563 (for K, we don't usually have units)

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