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chemistry igcse acapprinted 145 · PDF 145
145 pagesrevision 46934
printed 145 · PDF 145
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Increases
stays the same
decreases [1] Decreases
(ii) Is the forward reaction in the equilibrium 2SO2 + O2 ⇌ 2SO3 exothermic or
endothermic? Give a reason for your choice. [2]
It is exothermic, because increasing the temperature shifts the equilibrium backwards, so the backward reaction
is endothermic, therefore the forward one must be exothermic.
(iii) Explain, mentioning both rate and percentage yield, why the temperature used in
the Contact process is 450°C.[2]
It is 450°C because that is the ideal temperature that is low enough for a good yield and high enough for a
favourable economic rate.