Question

19) The thermite reaction given below is one of the most exothermic chemical reactions known. It is involved in a variety of industrial processes including welding. Iron (111) oxide is reduced at such a high temperature that the iron formed is in the liquid phase (MP = 1538*C). How much energy is evolved during the formation of 100.0g of Fe (55.85 g/mole)? Fe2O3(s) + 2Al(s) → Al2O3(s) +2Fe11 H rxn -852 kJ

Answer 1

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Given reaction:

$Fe_{2}O_{3}_{(s)}+2Al_{(s)}\rightarrow Al_{2}O_{3}_{(s)}+2Fe_{(l)}$

$\Delta H^{o}_{rxn}=-852\;kJ$

From the given reaction we have, 2 moles of Fe formation will result in -852 kJ of energy release:

$2\;mol\;Fe\rightarrow -852\;kJ$

$\therefore 1\;mol\;Fe\rightarrow \frac{-852\;kJ}{2}=-426\;kJ$

Given mass of Fe, m = 100 g

Therefore, no.of moles of Fe is given by,

$n=\frac{given\;mass}{molar\;mass}=\frac{100\;g}{55.85\;g/mol}$

$\boldsymbol{\therefore n=1.79\;mol}$

Therefore, Heat released during the formation of 100 g Fe is given by:

$E=1.79\;mol\;of\;Fe\times\left (426\;kJ/mol\;of\;Fe \right )$

$\boldsymbol{\therefore E=762.76\;kJ}$

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