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Effect of Product Concentration Adding products to a reaction in equilibrium will shift the equilibrium to the left, resulting in the formation of additional reactant. Likewise, removal of product shifts the reaction to the right, resulting in the formation of additional product. Consider the ionization of acetic acid:   If a strong acid is added to an equilibrium mixture of acetic acid, hydrogen ions and acetate ions, more acetic acid will be formed. This will also happen if a salt containing the acetate ion, such as sodium acetate, is added. In the latter case the pH of the solution will decrease, graphically demonstrating the equilibrium shift to the left. Note how the expression for Keq predicts this as well. Adding acetate ion is like adding stuff to the numerator. The only way the equilibrium constant can remain a constant, is for stuff from the numerator (products) to disappear and "move" to the denominator (reactants). The remarkable thing is that nature is smart enough to obey simple equations like these.

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