5.27 describe the manufacture of sulfuric acid by the contact process, including the essential conditions

(stage 1) S + O2 > SO2 
(stage 2) SO2 + O > SO3
(satge 3) SO3 + H2O > H2SO4

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i) a temperature of about 450C

ii) a pressure of about 2 atmospheres

iii) a vanadium(V) oxide catalyst (in stage 2)

Very helpful source:
http://namedorganicreactions.co.uk/Sulphuric.pdf