Chemistry 30

When iron rusts in air, the following reaction occurs:

4 Fe _(s) + 3 O_{2 (g)} → 2 Fe₂O_{3 (s)}    ΔH = -1643 kJ

What is the heat of formation, ΔH_f, of Fe₂O₃?

(hint: what is the heat of formation reaction for Fe₂O₃? How does this reaction compare to the reaction given in the question?)

The equation for the decomposition of mercury(II) oxide is as follows:

2 HgO _(s) + 182 kJ → 2 Hg _(l) + O_{2 (g)}

Determine ΔH_f for HgO _(s) ?

(hint: What does ΔH_f mean? What would be the overall equation associated with ΔH_f ?)

Calculate ΔH ° for the process:

2 Al(s) + Fe₂O_{3 (s)} → Al₂O_{3 (s)} + 2 Fe _(s)

Given that ΔH_f° of Fe₂O₃ = -813.0 kJ/mole and ΔH_f° of Al₂O₃ is -1,655.0 kJ/mol

The standard heats of formation for CH₄, CHCl₃ and HCl are -74.8, -132, -92.0 kJ/mole, respectively. Use this information to calculate the heat of reaction for the following reaction:

CH₄ + 3 Cl₂ → CHCl₃ + 3 HCl

The standard heat of formation, ΔH_f, for C₂H₄ is +52.3 kJ/mol. If C₂H₄ (ethylene) reacts with H₂ to produce C₂H₆ (ethane) according to the following equation:

C₂H₄ + H₂ → C₂H₆   ΔH = -137 kJ

what is the heat of formation of C₂H₆?

(Hint : Solve this question without looking up ΔH_f° for C₂H₆ in the Table of Thermochemical Data, although you may want to in order to check your answer. Solve this using the standard formula, ΔH reaction = ∑ ΔH products - ∑ ΔH reactants. However, this time you know ΔH reaction and need to solve for a substance on the product side of the equation.)

Using bond enthalpies, calculate ΔH for the following reaction:

N₂ + 2 H₂ → N₂H₄

The structural formulas for all reaction participants are shown here:

The energy from the combustion of hydrazine, N₂H₄ , is used to power rockets into space in the reaction:

N₂H₄ (g) + O₂ (g) → N₂ (g) + 2 H₂O (l)    ΔH ° = -627.6 kJ/mol

How many kilograms of hydrazine would be necessary to produce 1.0 × 10⁸ kJ of energy?

Hint: One mole of N₂H₄ produces 627.6 kJ of energy. How many moles (and then grams) are required to produce 1.0 × 10⁸ kJ of energy?