The Student Room Group


A thermite reaction is 2Al + Fe2O3 = Al2O3 + 2Fe

Calculate the heat of reaction (ΔH, J), the exothermicity (q, J kg-1) and the percentage of aluminium in the stoichiometric mixture given the heat of formation of the oxides are ΔH = -823 kJ mol-1 (Fe2O3) and ΔH = -1676 kJ mol-1 (Al2O3). The atomic mass of Al is 27 and the molecular mass of Fe2O3 is 160. [5 marks]
Calculate the adiabatic temperature of the reaction (mixture initially at 20°C) given that:

Average specific heat (20°C - 660°C) (kJ kg-1 K-1)
Al. Fe2O3. Al2O3
1.055 0.871 1.073
Average specific heat (660°C - 2520°C) (kJ kg-1 K-1)
Al. Fe2O3. Al2O3
1.181 0.982 1.474
Latent heat of fusion (660°C) (kJ kg-1)
Latent heat of vaporization (2520°C) (kJ kg-1)

It is observed that the burning rate of a pellet of the thermite varies with ambient pressure (faster at high pressure). The burning rate of the pellet containing the thermite diluted with Al2O3 (in the ratio 70/30) is slower and does not vary with applied pressure.

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