Given that: 2Fe(s)+32O2(g)⟶Fe2O3(s);ΔH=−193.4kJ...(i) Mg(s)+12O2(g)⟶MgO(s);ΔH=−140.2kJ....(ii) What is ΔH of the reaction? 3Mg+Fe2O3⟶3MgO+2Fe
A
−227.2kJ
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B
−237.3kJ
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C
2227.2kJ
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D
−257.3kJ
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Solution
The correct option is A−227.2kJ Eq.(ii) multiplied by 3, 3Mg+Fe2O3⟶3MgO;ΔH=−420.6kJ...(iii) 2Fe(s)+32O2(g)⟶Fe2O3(s);ΔH=−193.4kJ...(i) Subtracting (i) from (iii) 3Mg+Fe2O3⟶3MgO+2FeΔH=−420.6−(−193.4) =−227.2kJ