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Equipartition Theorem

Δ H∘f of Fe...

Question

$Δ H_{f}^{\circ}$ of $F e_{2} O_{3}$ and $A l_{2} O_{3}$ are -189 kJ and -405 kJ respectively. How much heat (in kJ) is given out during reaction of 1 g Al according to
$2 A l + F e_{2} O_{3} ⟶ A l_{2} O_{3} + 2 F e$ ?

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Solution

The enthalpy change for the reaction is,
$Δ H = Δ H_{f, A l 2 O 3} + 2 Δ H_{f, F e} - [2 Δ H_{f, A l} + Δ H_{f, F e 2 O 3}]$

$= - 405 k J / m o l + 2 (0 k J / m o l) - [2 (0 k J / m o l) - 189 k J / m o l] = - 216 k J / m o l$

The heat given out during reaction of 1 g Al is $\frac{- 216 k J / m o l}{2 \times 27 g / m o l} = - 4 k J / g$

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2 A l + F e_{2} O_{3} ⟶ 2 F e + A l_{2} O_{3}

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