[ecal]

Can anyone help me to explain what is Le Chatelier's principle?I couldnt understand the concept of temperature changes and pressure changes of its principle.can anyone explain to me in easier way? :1eye: :1eye:

[Mitch]

Be more specific. Give an example.

[ecal]

Do you know  how to determine the equilibrium position using the principle?What happen as  
the total pressure  of an equilibrium mixture increase by decreasing the volume?Generally how to determine which site will the equilibrium moves as some of the factors change.e.g(pressure,temperature)

[Grumples]

le chat's principle states that if a state at equilibrium is stressed, then the equilibrium will shift to counteract that stress.  For instance, if pressure is increased, the reaction will shift so as to reduce the amount of gas, which would thereby reduce the pressure.  i.e:

2NO2_(g) <-----> N204 _(g) + heat

If the pressure is increased, the reaction will shift to the right, because that will mean that there are fewer gas molecules aroundb (two moles on the left versus one on the right).  fewer gas molecules mean less pressure, so the change is cancelled.  if the system is heated, then the reaction will shift to the left, because the reverse reaction is endothermic, and will therefore cancel out the heat change.  Obviously, if more reactant or product is added, then the reaction wil shift to consume that addition; and if some is taken away, then the reaction will shift to create more of it.

Does that help?

[ecal]

Thanks dude!I think your explanation is much more woth it than my book.OK.Let me guess.The equil.position will change to the site (left or right) which experinece the less effect of the changes right?Therefore by change its position to opposite site,the equation or the chemical changes will be balanced.Rite?

[ksr985]

The key is that the reaction tries to oppose any external change that is made. If you increase the temperature, it will try move in the direction that will help it consume heat, or lower the temperature. if you increase pressure, the reaction will progress such that the amount of gas released is less..
this is just an easy way to figure out how to decide which way the reaction will go..the principle can be derived thermodynamically.

eg.

A + 2B <----> 3C + 4D    delta H<0 (ie, exothermic rxn)

now if you increase temp, the reaction will ty to decrease it, and move in the endothermic direction, that is, backward. if you decrease temp, the opposite will happen.

if you increase pressure, the reaction will progress such that the gas released is less.. in the forward direction, 7 moles are released, while in the backward direction, 3 moles are released. Therefore, on increasing pressure, the reaction will move in the backward direction. Keeping in mind that if the amount of gas released is more, the pressure in the container will increase.