What is the law of mass action? What determines the direction of a chemical reaction in a formula equation?
The law of mass action states that any reversible chemical reaction will reach a state of dynamic equilibrium when the ratio of concentrations of products to reactants is equal to a specific constant for that reaction called the equilibrium constant.
The equilibrium constant for this reaction, when concentrations are expressed in mol/L, is
If the equilibrium concentration of
However, if we double the equilibrium concentration of
The direction of spontaneous chemical reaction depends on whether the experimental ration of concentrations is greater than or less than the equilibrium constant. For any particular system (not at equilibrium, we can define the ratio of concentrations (products divided by reactants) to be Q. In the example above