2Fe2O3 –> 4Fe + 3O2

∆Hrxn° = +824.2 kJ

The decomposition of 29.0 g of Fe2O3 results in

a. the release of 150 kJ of heat

b. the release of 12000 kJ of heat

c. the absorption of 12000 kJ of heat

d. the absorption of 150 kJ of heat

e. the absorption of 74.8 kJ of heat

f. the release of 74.8 kJ of heat

The sign of dH is +; therefore, it must be an absorption of energy. Calculate how much. It should be one of c,d,or e.

(Amount of grams of Fe₂O₃ decomposed) x (1 mol Fe₂O₃/ Molar mass of Fe₂O₃ in grams) x (824.2 kJ/2 mol Fe₂O₃)

= 36.0 g Fe₂O₃ x (1 mol Fe₂O₃/ 159.69 g Fe₂O₃) x (824.2 kJ/2 mol Fe₂O₃)

= (29.0 x 824.2)/(159.69 x 2)

= 74.83812386 kJ

Since the sign of ΔH is positive, energy is absorbed.

The correct answer is E, which is the absorption of 74.8 kJ of heat.

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