Question

An intimate mixture of ferric oxide, $F{e}_2{O}_3$, and aluminium, Al, is used in solid fuel in rockets. Calculate the fuel value (in Kcal) per cc of the mixture. Heats of formation and densities are as follows : $H_f\left(A{l}_2{O}_3\right)=399$ kcal/mol, $H_f\left(F{e}_2{O}_3\right)=199$Kcal/mol, density of $F{e}_2{O}_3=\frac{16}{3}gm/cc$, density of Al = 2.7 gm/cc,

• A. 4
• B. 5
• C. 6
• D. 8

Answer 1

The correct option is A 4

Reaction:

$2Al+F{e}_2{O}_3\to 2Fe+A{l}_2{O}_3,\Delta H=-200Kcal$
Volume of fusion mixture $=\frac{54}{2.7}+\frac{160}{\frac{16}{3}}=50ml$
$\because$ 50 ml mixture produces 200 Kcal
$\therefore$ 1 ml mixture produces $=\frac{200}{50}=4Kcal.$