A) ? 1802 kJ
B) +1802 kJ
C) ? 800 kJ
D) + 228 kJ
Correct Answer: D
Solution :
\[2Fe+\frac{3}{2}{{O}_{2}}\to F{{e}_{2}}{{O}_{3}};\,\Delta H=-193.4\,kJ\] .....(i) \[Mg+\frac{1}{2}{{O}_{2}}\to MgO;\,\,\Delta H=-140.2\,kJ\] .....(ii) On multiplying eq. (ii) by 3 \[3Mg+\frac{3}{2}{{O}_{2}}\to 3MgO;\,\,\Delta H=-420.6\,kJ\] ......(iiii) Resulting equation can be obtained by subtracting eq. (i) from (iii) \[3Mg+\frac{3}{2}{{O}_{2}}\to 3MgO;\,\,\Delta H=-420.6\,kJ\] \[2Fe+\frac{3}{2}{{O}_{2}}\to F{{e}_{2}}{{O}_{3}};\,\,\Delta H=-193.4\,kJ\] Subtraction : \[3Mg+F{{e}_{2}}{{O}_{3}}\to 2Fe+3MgO;\,\Delta H=-227.2\,kJ\]
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