ChemicalEquilibrium

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

Write the balanced equation for the reaction.

Write the equilibrium expression using the law of mass action.

List the initial concentrations.

Calculate "Q," and determine the direction of the shift to equilibrium.

Define the change needed to reach equilibrium, and define the equilibrium concentrations by applying the change to the initial concentrations.

Substitute the equilibrium concentrations ionto the equilibrium expression, and solve for the unknown.

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:

H_2(g) + I_2(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