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chemistry igcse acapprinted 126 · PDF 126
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reactants’ side and two moles on the products’ side. Therefore, increasing the pressure will shift the equilibrium
forward and decreasing will shift it backwards
Catalyst: This has no effect whatsoever on the equilibrium’s position. It will increase the rate of reaction, but it
will not affect the position.
In addition to these, there are other factors to consider as well for the reactions involving copper (II) sulfate and
cobalt (II) chloride in your syllabus. In their reactions, the hydrated substance reacts in the forward reaction to
form its anhydrous form and water, with the opposite happening in the backwards reaction.
Adding water: This shifts the equilibrium backwards, to form more of the hydrated compound.
Heat: This shifts the equilibrium forward, as both hydrated substances decay in the presence of heat
The Haber Process (The Formation of Ammonia)
N2(g) + 3H2(g) ⇌ 2NH3(g
Sources of Reactants: Hydrogen is produced from methane and nitrogen from distillation of liquid air.
Conditions: 450°C, 20000kPa /200 atmospheres and an iron catalyst (remember that the catalyst has no effect
on the position of the equilibrium.)
The Contact Process (Conversion of Sulfur Dioxide to Sulfur Trioxide):
2SO2(g) + O2(g) ⇌ 2SO3(g)
Sources of Reactants: Sulfur dioxide is produced by burning sulfur or roasting sulfide ores. Oxygen is produced
by the distillation of liquid air.
Conditions: 450°C, 200kPa /2 atmospheres and a vanadium oxide catalyst (remember that the catalyst has no
effect on the position of the equilibrium.)
Why are the conditions for both processes like this?
In both cases, the forward reaction is exothermic, so increasing the temperature leads to a decrease in yield by
shifting the equilibrium backwards. However, decreasing the temperature would lead to a decrease in the rate, so
these temperatures have been chosen to keep both factors in a desirable range.
In both cases, the products have less gaseous moles, so increasing the pressure increases the yield by shifting the
equilibrium forward as well as the rate of reaction. However, high pressures can require a lot of effort and
equipment to maintain, so they are not infinitely high.