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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Topic 2.3

EQUILIBRIA

Dynamic Equilbria
Le Chatelier's Principle
Industrial Equilibria
























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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…

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2. 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…

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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…

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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…

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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…

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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…

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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…

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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)…

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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…

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