EXAMPLE Calculating Equilibrium Pressures:
which has been used as a refrigerant and a local anesthetic, can be made
from the following reaction.
If enough methanol and
hydrogen chloride are added to a container at 120 C to yield an
initial pressure of 0.75 atm for each, what will the equilibrium
pressures of all of the reactants and products be?
start by writing the equilibrium constant expression that corresponds to
the given chemical equation:
Next, we set up a table describing the initial gas
pressures, the changes in pressures, and the equilibrium pressures in
terms of x. For our problem, we assign "x" to the decrease in
pressure of CH3OH and HCl.
We now plug in the terms for the equilibrium concentrations of each
reactant and product into the equilibrium constant expression.
Next, we solve for x. (We can simplify our equation by taking the square
root of both sides.)
We complete the
problem by calculating the equilibrium concentrations of each reactant
and product from the calculated x.