In this section equilibrium pressures are calculated from known
initial concentrations of all components and the
known equilibrium constant for the reaction.
The general method used in solving such problems is outlined below:
- Write the expression for K that applies to the given system.
- Construct a table having rows labelled initial, change and final (equilibrium) with a column for each component appearing in the reaction quotient.
- Enter given data. For components having no "initial pressure" mentioned in the problem, enter 0.
- Take x as the change in concentration of one substance. Express the changes in the other substances appearing in the reaction quotient in terms of x.
- Obtain expressions for equilibrium concentrations in terms of x.
- Substitute into the reaction quotient expression. Set this expression equal to the equilibrium constant.
- Solve for x.
The solution for x depends on the form of the resulting equation.
The maths can get quite complicated. Don't worry about this.
It is the chemistry in steps 1-6 that should be emphasized.