Equilibrium Le Chatelier’s Principle. Equilibrium Brown gasColourless gas.
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Transcript of Equilibrium Le Chatelier’s Principle. Equilibrium Brown gasColourless gas.
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Equilibrium
Le Chatelier’s Principle
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Equilibrium
Brown gasColourless gas
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Equilibrium
Imagine we begin with a container that has only N2O4 gas. Some of these molecules will successfully collide and produce NO2.
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Equilibrium
The colour of the gas mixture will get browner as less N2O4 and more NO2 will be present, until equilibrium is achieved.
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Equilibrium
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Equilibrium
At equilibrium there will be NO2 and N2O4 present. The colour of the mixture will be determined by the amount of NO2 present.
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Equilibrium
At equilibrium the macroscopic properties, such as pressure and colour will be constant.
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Equilibrium
At equilibrium the forward and reverse reactions will both be occurring.
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Equilibrium
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Equilibrium expression
An equilibrium expression gives an indication of the relative amounts of products to reactants at equilibrium.
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Equilibrium expression
For this reaction the equilibrium expression is:
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Equilibrium expression
The square bracket represents concentration.
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Equilibrium expressionSolids and liquids do not have a concentration and therefore would not be included in the expression.
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Equilibrium expressionAny co-efficient in the balanced equation appears as an indice in the equilibrium expression.
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Equilibrium expression
The value for this particular reaction, at 100oC is always 0.21.
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Le Chatelier’s PrincipleIf a sy stem at eq u i l ibriu m has a chan g e im posed on i t, then the sy stem wi l l partial ly oppose the chan g e in su ch a way as to re-establ ish the eq u i l ibriu m .
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Le Chatelier’s Principle
If the equilibrium concentrations were
[NO2] = 0.205, [N2O4] = 0.2
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Le Chatelier’s Principle
and we added more N2O4 to bring it’s concentration up to 0.3 mol L-1. The system would adjust to get back to where K = 0.21
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Le Chatelier’s Principle
This would happen by trying to get the [N2O4] partially back to its original value. At the same time the [NO2] would increase.
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Le Chatelier’s Principle
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Le Chatelier’s Principle
The concentrations of each at the new equilibrium are:
[NO2] = 0.245 mol L-1
[N2O4] = 0.28 mol L-1
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Le Chatelier’s Principle
If at these new concentrations the volume of the container was halved:
What would be the new concentrations?
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Le Chatelier’s Principle
If at these new concentrations the volume of the container was halved:
What would happen to the pressure in the container?
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Le Chatelier’s Principle
When pressure increases Le Chatelier’s principle says that the system will try to partially restore the original pressure.
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Le Chatelier’s Principle
This could be achieved by favouring the reaction which produces fewer gas molecules. ie reverse reaction
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Le Chatelier’s Principle
0oCroom temp
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Le Chatelier’s Principle
Lowering the temperature favours the reverse reaction, since the mixture gets lighter in colour.
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Le Chatelier’s PrincipleWhy?
What does Le Chatelier predict will happen when you lower the temperature of a system.
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Le Chatelier’s PrincipleThe principle predicts that the reaction will try and increase the temperature. It can do this by producing heat. ie an exothermic reaction would be favoured.
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Le Chatelier’s PrincipleThe reaction will attempt to re- establish its original equilibrium but will not be able to . The equilibrium constant for a reaction is only constant at one temperature.
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Le Chatelier’s PrincipleAt room temperature
At zero degrees
[N2O4] 0.049 0.098
[NO2] 0.102 0.005
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Le Chatelier’s Principle