Solid fuel used in rocket is a mixture of Fe 2 O 3 and Al (in ratio 1 : 2 ). The heat evolved ( kJ ) per gram of the mixture is _____ (Nearest integer) Given ΔH f 0 Al 2 O 3 = - 1700 kJ mol - 1 ΔH f 0

Question

Solid fuel used in rocket is a mixture of ${Fe}_{2} O_{3}$ and $Al$ (in ratio $1 : 2$ ). The heat evolved $(kJ)$ per gram of the mixture is _____ (Nearest integer)

Given ${ΔH}_{f}^{0} ({Al}_{2} O_{3}) = - 1700 kJ {mol}^{- 1}$

${ΔH}_{f}^{0} ({Fe}_{2} O_{3}) = - 840 kJ {mol}^{- 1}$

Molar mass of $Fe, AI$ and $O$ are $56, 27$ and $16 g {mol}^{- 1}$ respectively

TestHub · Accepted Answer

Molten iron can be prepared by alumino thermite process as shown below.

${Fe}_{2} O_{3} + 2 Al \to 2 Fe + {Al}_{2} O_{3}$

The iron oxide and aluminium metal ratio is $1 : 2$ in the above reaction.

Now, the Enthalpy of the reaction is equal to the difference of enthalpy of formation of products to the enthalpy of formation of reactants.

${ΔH}_{reaction}^{0} = - 1700 + (840)$

Ratio of ${Fe}_{2} O_{3}$ and $Al$

$= 160 : 54$

$= 2.96 in 214 gm$ mixture

$∴ \frac{ΔH °}{1 gm mixture} = \frac{- 860}{214} = - 4 kJ / gram$

Chemistry - Thermochemistry Question with Solution | TestHub

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