Chemical Thermodynamics Question 312
Question: Given : $ 2Fe+\frac{3}{2}O_2\to Fe_2O_3,,\Delta H=-193.4,kJ $ ; $ Mg+\frac{1}{2}O_2\to MgO,,\Delta H=-140.2,kJ $ What is the $ \Delta H $ of the reaction $ Mg+Fe_2O_3\to 3MgO+2Fe $ [Orissa JEE 2005]
Options:
A) - 1802 kJ
B) +1802 kJ
C) - 800 kJ
D) + 228 kJ
Show Answer
Answer:
Correct Answer: D
Solution:
$ 2Fe+\frac{3}{2}O_2\to Fe_2O_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 Fe_2O_3;\Delta H=-193.4,kJ $
Subtraction : $ 3Mg+Fe_2O_3\to 2Fe+3MgO;,\Delta H=-227.2,kJ $
