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 $



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