Editing revision 18 of ChemicalEquilibrium

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Here are the basic procedures for solving equilibrium problems: (from Zumdahl textbook)

<li>Write the balanced equation for the reaction.
<li>Write the equilibrium expression using the law of mass action.
<li>List the initial concentrations.
<li>Calculate "Q," and determine the direction of the shift to equilibrium.
<li>Define the change needed to reach equilibrium, and define the equilibrium concentrations by applying the change to the initial concentrations. 
<li>Substitute the equilibrium concentrations ionto the equilibrium expression, and solve for the unknown. 
<li>Check your calculated equilibrium concentrations by making sure they give the correct value of "K."

Examples:

1. Assume that the reaction for the formation of gaseous hydrogen iodide from hydrogen and iodine has an equilibrium constant of 2.3 x 102. In an experiment, 4.0 mol of each participant in the reaaction was added to a 2.0 L flask. Find the equilibrium concentrations of all species involved in this reaction.

The balanced equation for the reaction is:

H2(g) + I2(g) <--> 2HI(g)

The equilibrium expression is:

K = 2.0 x 102 = [HI]2 / [H2][I2]

First, you must calculate the initial concentrations. In this case, all of the species' concentrations will be equal to each other.

[HI]0 = [H2]0 = [I2]0 = 4.0 mol / 2.0 L = 2.0 M

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