Question
Fri February 08, 2013 By:

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Expert Reply
Sat February 09, 2013

The le Chatelier's principle is stated as:

When external stress is applied on a system at dynamic equilibrium, the system shifts the position of equilibrium so as to nullify the effect of stress. 

Stress can be applied on chemical systems by changing the concentration or pressure or temperature. Therefore the le Chatelier's principle can also be stated as:

When a chemical system at dynamic equilibrium is disturbed by changing the concentration of either reactants or products; or by changing the partial pressures of any of gaseous reactants or of gaseous products; or temperature, the position of equilibrium is changed in that direction so as to establish a new equilibrium state i.e., either forward reaction or backward reaction is favored.

By using le Chatelier's principle, the effect of change in concentration on systems at equilibrium can be explained as follows:

1) When the concentration of reactant(s) is increased, the system tries to reduce their concentration by favoring the forward reaction.

2) When the concentration of product(s) is increased, the system tries to reduce their concentration by favoring the backward reaction.

3) When the concentration of reactant(s) is decreased, the system tries to increase their concentration by favoring the backward reaction.

4) When the concentration of product(s) is decreased, the system tries to increase their concentration by favoring the forward reaction.


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