The thermite reaction involves aluminum and iron (III) oxide as shown here:

Question

2Al(s) + Fe2O3(s) Al2O3(s) + 2Fe(l).
This reaction is highly exothermic and the liquid iron formed is used to weld metals.
Calculate the heat released in kilojoules per gram of Al reacted with Fe2O3. The standard
enthalpy of formation (ΔHof) for Fe(l) is 12.40 kJ/mol.
Note: For the ΔHo
f for other substances, check on internet or at the appendix of any chemistry
text books.

Answer 1

To calculate the heat released per gram of aluminum reacted, we first need to determine the moles of aluminum reacting with iron (III) oxide.

From the balanced chemical equation, we see that 2 moles of aluminum react with 1 mole of iron (III) oxide.

Molar mass of Al = 26.98 g/mol
Molar mass of Fe2O3 = (55.85 x 2) + (16 x 3) = 159.69 g/mol

Let x be the moles of Al reacting.
From the equation:
2x moles of Al = 1 mole of Fe2O3
x = 0.5 moles

Now, calculate the heat released in the reaction:
ΔH = ΔHof(Al2O3) + ΔHof(Fe) - ΔHof(Fe2O3)
= 0 + 12.40 kJ/mol - [(-824.2) + (-394.4)] kJ/mol
= 12.40 kJ/mol + 1218.6 kJ/mol
= 1231.0 kJ/mol

Now, calculate the heat released per gram of Al:
Heat released = ΔH/n
= 1231.0 kJ/mol / 0.5 mol
= 2462.0 kJ/mol

Therefore, the heat released per gram of Al reacted with Fe2O3 is 2462.0 kJ/g.