Le Chatliers principle

[theMaharajah]

Anyone got any advice on solving equilibrium problems with Le Chatliers principle...

 

also any explanations of shifts in eqiulibrium reactions would be greatly apprecaited!

[encipher]

You can't use Le Chatelier's principle to actually SOLVE equilibrium problems. What the Le Chatelier principle does is predict which direction the equilibrium will shift to. For example:

 

2NOCl <---> 2NO Cl2

 

If the pressure on the system increased, which direction would this equilibrium shift to? According to Le Chatelier's principle, if a change is imposed on a system at equilibrium , the position of the equilibrium willl shift in a direction that tends to reduce that change. In this case, the equilibrium will shift to the left because there are less particles of NOCl then there are NO and Cl2.

 

 

Another good example would be a flask filled with NO2

 

 

equilibrium expression:

 

2 NO2 (g) <=> N2O4 (g) + Heat

 

If you cool down the flask it turns pale/light colored forming N2O4. if you heat it up you get a deep reddish brown color NO2.

[Tartaglia]

Le Chatalier's principle can of course in certain circumstances be given in a mathematical form. eg the Van't Hoff equation is a statement of how the equilibrium constant varies with change in temperature and is basically a mathematical version of Le Chatalier's Principle

 

d(lnK)/dT = deltaH/RT^2

 

This allows quantitative as well as qualitative evaluation of the change of temperature on the eqm position