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
Next, find the value of Q (initial conditions):
Q = [HI]20 / [H2]0[I2]0 = (2.0 M)2 / (2.0 M)(2.0 M) = 1.00
Since Q is less than K, the system will shift to the right (towards the products).