CONTACT PROCESS
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What is the purpose of the contact process?
Sulphuric acid
What do we use sulphuric acid for?
Cleaning agents Fertilizers Paint
What are the raw materials used in the contact process?
Oxygen (in the air) Sulphur Water
What is the chemical formula of sulphuric acid?
H2SO4
What are the conditions needed for the contact process?
2 atmospheres 450˚
What is the catalyst used in the contact process?
Vanadium (V) oxide
What are the two ways you can introduce sulphur into the equation?
Pure sulphur Sulphide ore (FeS2) also called pyrite
What is the equation for the first stage of the contact process using pure sulphur?
S(s) + O2(g) –> SO2(g)
What type of reaction is the first stage of the contact process (S(s) + O2(g) –> SO2(g))?
Oxidation reaction Combustion reaction
What is the equation for the alternative first stage of the contact process using pyrite (sulphide ore)?
4FeS2(s) + 11O2(g) –> 2Fe2O3(s) + 8SO2(g)
What is the equation of the second stage of the contact process?
2SO2(g) + O2(g) 2SO3(g)
Why must the second stage of the contact process be done in excess air?
To shift the reaction to the right and hence increase the amount of SO3 produced.
Is the second stage of the contact process exothermic or endothermic?
Exothermic (∆H= -196 kJ/mol)
As the second stage of the contact process is exothermic, theoretically would it be better to do this reaction at high or low temperatures?
Low temperature
So if the second stage of the contact process would have a higher yield at a lower temperature, why do we do the reaction of 450˚?
Because the rate of the reaction would be too slow at a lower temperature. 450˚ is the compromise.
Why do we do the reaction at 2 atmospheres?
Because there are 3 moles on the left side of the equation and there are 2 moles on the right. The right is therefore preferred at higher pressures. Therefore increasing the pressure will shift the reaction to the right.
Does the catalyst increase the yield?
No. A catalyst never increases the yield. It only increases the rate.
How does a catalyst work?
It provides an alternative pathway with a lower activation energy.
What is activation energy?
The minimum amount of energy for the reaction to take place.
What is the reaction in the third stage of the contact process?
SO3(g) + H2SO4(l) –> H2S2O7(l)
What is another name for H2S2O7?
Oleum
What is the equation for the fourth stage of the contact process?
H2S2O7(l) + H2O(l) –> 2H2SO4(aq)