# Equilibria

This is not mine, it is from this lovely website here:
http://www.a-levelchemistry.co.uk

They are from the AQA section but are useful to anyone that does equilibria in their A-level

These notes go into more detail than is necessary, and I am hoping to upload condensed versions soon :)

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• Created by: Megan1808
• Created on: 31-05-13 18:29

First 16 words of the document:

Topic 2.3
EQUILIBRIA
Dynamic Equilbria
Le Chatelier's Principle
Industrial Equilibria

## Other pages in this set

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REVERSIBLE REACTIONS
1. Dynamic equilibria
Consider a reversible reaction A + B == C + D
As the reaction proceeds, the rate of the forward reaction decreases and the rate of the reverse
reaction increases. Eventually, the reaction will reach a stage where both forward and backward
reactions are proceeding at the same rate:
At this stage, a dynamic equilibrium has been reached. "Dynamic" means that the reaction has
not stopped it is simply moving in both directions at the same rate.…read more

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Open and closed systems
A closed system is one from which reactants and products cannot escape. In closed systems
the forward and reverse reactions continue until dynamic equilibrium is reached. All reactions in
a closed system are thus reversible in theory, although they are only considered as such if both
forward and reverse reactions occur to a significant extent.
Eg H+(aq) + OH(aq) H2O(l)
In this case the reverse reaction is not significant so the reaction is represented by single arrow.…read more

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Each must be treated separately:
1. Concentration
Le Chatelier's principle predicts that if a reactant's concentration in a system is increased, the
system will move to the right in order to decrease the concentration of that reactant. If the
reactant's concentration is decreased, the system will move to the left in order to replace that

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If the pressure is increased, the system will move to the right, where there are fewer moles. If
the pressure is decreased, the system will move to the left, where there are more moles.
Eg 2H2S(g) + SO2(g) == 3S(s) + 2H2O(l)
If the pressure is increased, the system will move to the right, where there are fewer moles.…read more

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Eg CaCO3(s) == CaO(s) + CO2(g), H = +ve
An increase in temperature will favour the endothermic direction in order to decrease the
temperature, so the reaction will proceed to the right. A decrease in temperature will favour the
exothermic direction in order to increase the temperature, so the reaction will proceed to the
left.
In summary: When the temperature is increased, the system will move in the
endothermic direction in order to decrease the temperature.…read more

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INDUSTRIAL EQUILIBRIA
Many largescale industrial processes involve reversible reactions. These reactions do not go to
completion but reach an equilibrium. The position of this equilibrium depends on the conditions
employed, and Le Chatelier's principle can be used to predict the conditions which will
maximise the amount of product formed.
The position of equilibrium, however, is not the only factor which must be considered when
choosing the best conditions for an industrial reaction.…read more

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Catalysts increase the rate of reaction without affecting the position of equilibrium. This reaction
therefore takes place in the presence of a catalyst, V2O5. The catalyst ceases to become
effective at very low temperatures, and this places a further constraint on the minimum
temperature which can be used in the reaction.
The optimum conditions for this reaction are 400oC and a little above atmospheric pressure.
Under these conditions 98% yield is achieved.…read more

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The optimum conditions for this reaction are 450oC and a pressure of 200 atm. Under these
conditions a 15% yield is achieved. The unreacted nitrogen and hydrogen are recycled.
(c) The production of ethanol
Most ethanol produced for industrial purposes is manufactured by the reaction of ethene with
steam:
H2C=CH2(g) + H2O(g) C2H5OH(g)
This reaction is also exothermic.
Like the Haber Process and the Contact process, the best yield is obtained by using a low
temperature and a high pressure.…read more

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The yield achieved under these conditions is only 5% but, like in the Haber process, the
unreacted carbon monoxide and hydrogen can be recycled.
CARBON NEUTRALITY
A carbonneutral process is one which has no net carbon dioxide emissions into the
atmosphere.
The alcohols methanol and ethanol can both be burnt to release energy.
They are very useful fuels as they generally release less polluting gases than hydrocarbon fuels.
It is also possible, under certain circumstances, to use these fuels in a carbonneutral and