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Equilibria
6.1 The idea of Equilibria: 6.3 Equilibrium reactions in industry:
Equilibrium mixture: the point in a reversible reaction In industry you must find a balance between rate, yield
when the proportions of all components remain constant, and the cost of a reaction.
only in a closed vacuum. Making Ammonia (the Haber process)-
Dynamic equilibrium: when the rate of the forward and
backward reaction is constant and equal.
• must be in a closed system
• can be approached by either direction 1. Nitrogen and hydrogen based over a converter and
• equilibrium has been reached when no macroscopic iron catalyst
properties are changing 2. At a low pressure of 20,000kPa and a high
temperature of 670K to give the best yield.
3. The iron catalyst must be replaced every 5 years due
6.2 Changing the conditions of an equilibrium reaction: to gas poisoning
Due to the high temperature and the iron catalyst the rate
You can change the conditions to favour the forward or increases but will increase the cost of the reaction. Yet a
backward reaction. If the forward reaction is favoured, high temperature will favour the exothermic/ backward
equilibrium moves to the right . If the backward reaction reaction due to le Chatelier’s principle. A low pressure is
is favoured it moves to the left. used to move the equilibrium to the right to favour the
Le Chatelier’s principle: if a system at equilibrium is forward reaction, increasing the yield.
disturbed, the equilibrium moves in the direction that Ammonia is used to make fertilisers, nylon, explosives,
tends to reduce the disturbance drugs and dyes.
Making ethanol-
Increasing concentration of the reactants will move the
reaction to the right, as the concentration has increased
it will favour the forward reaction so the concentration
can be decreased again. Ethanol is used in alcohol, normally used by
Decreasing concentration of reactants, removing some fermenting glucose with yeast enzymes as a catalyst.
of the reactants decreases the concentration and so the Also used for cosmetics, drugs, detergents, inks and
equilibrium moves to the left, this is to favour the fuel. Industrially ethanol is produced by fractional
backward reaction so that more of the reactant can be distillation and cracking to produce ethene and then it’s
produced and increase the concentration again. hydrated. Catalysed by phosphoric acid absorbed on
silica.
Increasing pressure, only works on a reaction involving • high pressure moves equilibrium to the right to
gases. When you increase pressure it will favour the favour ethanol yield, the same as a low temperature
reaction that uses the most amount of moles. It will try as it’s exothermic and increasing the concentration
to use as many moles as possible to decrease the pressure. of steam so the equilibrium moves to reduce the
Decreasing pressure, will move equilibrium to favour the increase.
production of more moles of gas, this will increase their • A high pressure will cause ethene to polymerise and
concentration and so the pressure will increase again. it will increase the cost. A lower temperature will also
If there’s the same amount of moles of gas on each side decrease the rate of reaction as the particles have less
of equilibrium, changing the pressure will have no energy so there’s less successful collisions -
effect. although use of catalyst helps, yet too much steam
will dilute the catalyst which you also need to pay
Increasing temperature will favour the endothermic for.
reaction, this reaction will take in heat and cool the
system down. Making methanol-
Decreasing temperature will favour the exothermic
reaction which will give heat out to increase the
temperature and oppose the disturbance.
Methanol is used as chemical feedstock (starting
Catalysts will have no effect on the position of material for other reactions) and fuel. It will give the
equilibrium as it speeds up the rate of reaction for both highest yield at a low temperature and a high pressure
the forward and the backward reaction and so the but a comprise is used due to the cost, rate and the copper
system is still in a dynamic equilibrium. catalyst.
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