Talk:General Chemistry/Chemical Equilibria/Le Chatelier's Principle

Inaccurate statements

 * Le Chatelier's Principle states that when a system that is in dynamic equilibrium is disrupted in some way, the system will respond with chemical or physical changes to restore a new equilibrium state.

It is awkward to say the equilibrium is restored. The most important part is to realize that the manipulation (change in concentration or temperature) results in a non-equilibrium state. As a consequence, the reaction will go forward or backwards, and will reach equilibrium once more.


 * If the concentrations in a system are changed, Le Chatelier's Principle predicts that the equilibrium position will shift to minimize the change.

It is not clear what it means to minimize the change. If I double the concentration of a reactant, minimizing the change could be misread to mean that the concentration will return to the original concentration (which it generally does not do). It is correct to say that as the system reaches a new equilibrium, it partially reverts the changes imposed by the manipulation.


 * Change in Concentration 	System response
 * Increase reactant 	Favors products
 * Decrease reactant 	Favors reactants
 * Increase product 	Favors reactants
 * Decrease product 	Favors products

Favors product might be misread to mean that there is more product than reactant. What is does mean is that the reaction goes forward to reach a new equilibrium, i.e. product concentrations will rise as reactant concentrations decrease. However, we don't know whether the reactant or product concentrations are higher in the end (this depends on the value of the equilibrium concentration and the combination of initial concentrations).


 * The product side has higher pressure than the reactant side.

It is correct to say that if the reaction goes forward, the pressure will increase because more gas molecules are produced than used up. To say that the product side has a higher pressure than the reactant side is utterly confusing, as the reactants and products are present in a single gas mixture. You could make a statement about the sum of the partial pressures of the products compared to the reactants, but this depends on the initial partial pressures and can't be predicted from the balanced equation.


 * If an inert gas (such as neon) is added to a system, it will raise the overall pressure. However, the partial pressures of all products and reactants are unchanged, so no shift in equilibrium occurs.

This statement is wrong unless you specify that the volume is kept constant (as in a steel cylinder). If the pressure is kept constant (as in a gas tight syringe), the partial pressures do change upon adding an inert gas, and a shift will occur.

--Theislikerice (discuss • contribs) 20:09, 28 February 2012 (UTC)