The thermite reaction occurs when a mixture of powdered aluminum and iron(III) oxide is ignited with a magnesium fuse. Using enthalpies of formation, calculate the standard change in enthalpy for the thermite reaction:
2 Al(s) + Fe2O3(s) →Al2O3(s) + Fe(s)
Solution:
To calculate change in enthalpy for the reaction, ΔH, we can use enthalpies of formation given in the chart. We do the sum of enthalpies of formation of products - the sum of enthalpies of formation of reactants. We also need to include coefficients from the reaction.
Therefore we do ΔHrxn = (ΔHf Fe + ΔHf Al2O3(s)) - (ΔHfAl *2 + ΔHfFe2O3(s))
Let's plug in the numbers:
ΔHf Fe(s) and Al(s) are not shown in the table because they are 0. Enthalpies of formation of elements in their standard state are zero.
ΔHrxn = (0+(-1676kj/mol) - (2*0 + (-826kj/mol)) = -850 kj/mol