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About le chatelier principle.

thestars of night

3

Hey,could anyone understand me about le chatelier principle?I am unable to understand clearly.

Reply 1

hanh01

1

thestars of night

Hey,could anyone understand me about le chatelier principle?I am unable to understand clearly.

Le chatelier principle = whenever you change a condition of a system e.g. temperature/pressure/concentration, the system will oppose the change and favour the reaction where the change is opposed.

e.g. you have reversible reaction where the forward reaction is exothermic and produces heat.
If you increase the temperature, then system will oppose it and favour the reverse reaction which is endothermic and therefore uses up the extra heat that you put in.

hope this is clear :wink:

Reply 2

north bank gooner

The equilibrium in a system will shift to minimise the effect of any imposed changes.

If you increase the pressure in a reaction vessel, then this will favour the formation of the reaction direction which results in fewer molecules.
e.g. 3H2 + N2 --> 2NH3
increasing pressure will favour the forward reaction as this lowers the total number of molecules in the reaction mixture, therefore lowering pressure. So the equilibrium has shifted to counter the imposed change

Similarly, raising temperature will favour the endothermic reaction. The endothermic raction takes in heat, so the imposed change has been counteracted.

Reply 3

I_L_S

6

in the above example if u add more hydrogen to the mixture it moves the system away from hydrogen (reactant/ left) to 2NH3 (product/right).

Reply 4

ch0c0h01ic

18

I googled it and found this, it explains it pretty well:

http://www.chemguide.co.uk/physical/equilibria/lechatelier.html

Any other questions just ask.

Main principles:
1. Catalysts have no effect on the position of equilibrium because they speed up both the forward and backward reactions equally (so the quantity/ratio of the products on either side is unaffected).
2. Its a dynamic equilibrium, so changing the quantites/conditions of the substances on one side of the equilibrium will cause a shift to compensate (ie; increasing the concentration of the reactant on the left will cause a shift in the equilibrium to the right so that more products are formed, increasing the concentration of the products to compensate, and vice versa).
3. And its got to be a closed system to work.

Hope that helps its been a while since i've done IB chem.

Reply 5

thestars of night

OP

3

hanh01

Le chatelier principle = whenever you change a condition of a system e.g. temperature/pressure/concentration, the system will oppose the change and favour the reaction where the change is opposed.

e.g. you have reversible reaction where the forward reaction is exothermic and produces heat.
If you increase the temperature, then system will oppose it and favour the reverse reaction which is endothermic and therefore uses up the extra heat that you put in.

hope this is clear :wink:

If you don't mind,what you have told,I've already cleared about it.The thing I'm obscured in this principle is that,from your e.g (if enthalpy is input then the position of the equilibrium would shift in the reverse direction),but whats the cause behind it to reverse?It can be shift towards the forward reaction whilst enthalpy is input.Consider,
CH4 + O2 gives CO2 +H2O +E(ENTHALPY -VE)
if heat is given in the closed chamber why don't CO2 react with H2O while CH4 & O2 gets react.Whats the reason behind it for to react with only them not the CO2 & H2O?

Reply 6

thestars of night

OP

3

The thing I'm obscured in this principle is that,from your e.g (if enthalpy is input then the position of the equilibrium would shift in the reverse direction),but whats the cause behind it to reverse?It can be shift towards the forward reaction whilst enthalpy is input.Consider,
CH4 + O2 gives CO2 +H2O +E(ENTHALPY -VE)
if heat is given in the closed chamber why don't CO2 react with H2O while CH4 & O2 gets react.Whats the reason behind it for to react with only them not the CO2 & H2O?

Reply 7

hanh01

1

thestars of night

If you don't mind,what you have told,I've already cleared about it.The thing I'm obscured in this principle is that,from your e.g (if enthalpy is input then the position of the equilibrium would shift in the reverse direction),but whats the cause behind it to reverse?It can be shift towards the forward reaction whilst enthalpy is input.Consider,
CH4 + O2 gives CO2 +H2O +E(ENTHALPY -VE)
if heat is given in the closed chamber why don't CO2 react with H2O while CH4 & O2 gets react.Whats the reason behind it for to react with only them not the CO2 & H2O?

hmm... I dunno... Im desperately trying to find a reason now... Ive never thought about that but its really interesting...
tell you what, ive got chemsitry next lesson so i shall ask my teacher and tell you the answer. But its really interesting and perfectly reasonable question..! :redface:

Reply 8

Wangers

16

hanh01

hmm... I dunno... Im desperately trying to find a reason now... Ive never thought about that but its really interesting...
tell you what, ive got chemsitry next lesson so i shall ask my teacher and tell you the answer. But its really interesting and perfectly reasonable question..! :redface:

I would need to look at the da book values to be sure, but I would suspect its something to do with Entropy values and other Thermodynamic considerations; remember, the Principle states that:

if a change is imposed upon a closed system in dynamic equilibrium, the equilibrium position will shift so as to attempt to minimise the effect of the change.

Therefore it follows that the system does not need to bend over backwards to reverse the change per se to satisfy the conditions.

Reply 9

thestars of night

OP

3

hanh01

hmm... I dunno... Im desperately trying to find a reason now... Ive never thought about that but its really interesting...
tell you what, ive got chemsitry next lesson so i shall ask my teacher and tell you the answer. But its really interesting and perfectly reasonable question..! :redface:

Surely,u can ask question to your teacher.I'm also curious too.I'll be waiting for your answer.

About le chatelier principle.

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