The heat of formation of Al2O3(s) is change Hf= -1669kJ/ /mol. a.) Calculate the

Question

The heat of formation of Al2O3(s) is change Hf= -1669kJ/ /mol. a.) Calculate the heat evolved when 3.47 g of Al burns in oxygen. b.) Find the mass in grams of Al that burns when 1039 kJ are evolved.

Explanation / Answer

You will need a table of delta Hf, enthalpies (heats) of formation of compounds: 2Al(s) + 1.5O2(g) -----> Al2O3(s) Enthalpy of formation of Al2O3 = -1676 kJ ./ mol (this is from my book, Zumdahl 5th ed.) So this is also the ethalpy (heat) of formation, which is the energy released or absorbed in the formation of one mole of a compound. So in this case the enthalpy of combustion and the enthalpy of formation are the same. Remember the enthalpy of formation of the elements is zero.

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