Le Chatelier's Principle - Shifting Equilibrium Position

Hello,

 This post is a discussion of effects on the positions of equilibria resulting from changing reaction conditions. 

 There are three general situations to cover here; solution equilibria, gas-phase equilibria and temperature change effects. Solution equilibria positions change with changing reactant or product concentrations whereas gas phase equilibria positions are effected by changing pressure.  Temperature effects depend on whether an equilibrium reaction absorbs or releases heat and whether temperature is increased or decreased.  This post focuses on solution equilibria position changes.  My next two posts will cover the effects of changing temperature and pressure conditions.

Le Chatelier's Principle

In 1884, the French Chemist, Henry-Louis Le Chatelier revealed the results of his ground-breaking research on the behavior of chemical equilibria systems.  In general, Le Chatelier's findings tell us that if quantities in a chemical equilibrium system (of either equilibrium species or external temperature) are varied, we can expect the equilibrium position to shift in a direction which will reduce the effect of the change.  The following figure shows how the position of a solution equilibrium changes back to its initial state with an increase in reactant concentration.

As you can see from the figure the concentrations of reactants and products, compared with each other, returns after the equilibrium is "upset" by adding more reactant solute.  The change in equilibrium position is indicated with a change in the length of the top arrow and changing reactant/product shape sizes (indicating changing concentrations).  My next post will focus on the effect of changing equilibrium system temperature.

Have a good one!



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