ThermochemistryHard
Question
The enthalpies of formation of FeO(s) and Fe2O3(s) are −65.0 and −197.0 kcal/mol, respectively. A mixture of the two oxides contains FeO and Fe2O3 in the mole ratio 2:1. If by oxidation it is changed in to a 1:2 mole ratio mixture, then how much of thermal energy will be released per mole of the initial mixture?
Options
A.13.4 kcal
B.67 kcal
C.47.2 kcal
D.81 kcal
Solution
$2FeO + \frac{1}{2}O_{2} \rightarrow Fe_{2}O_{3};\Delta H = ( - 197) - 2( - 65) = - 67\text{ kcal}$
Initial $2a a$
Final $2a - 2x a + x$
$\frac{2a - 2x}{a + x} = \frac{1}{2} \Rightarrow x = \frac{3}{5}a$
and heat released = 67x kcal
∴ Heat released per mole of initial mixture = $\frac{67x}{3a} = 13.4\text{ kcal}$
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