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Ethanol is a possible fuel. Use average bond energies to calculate ΔHrxn for the combustion of ethanol. CH3CH2OH(g) + 3 O2(g) → 2 CO2(g) + 3 H2O(g) Express your answer as an integer.

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Explanation:

The reaction is as follows.

       [tex]CH_{3}CH_{2}OH(g) + 3O_{2}(g) \rightarrow 2CO_{2} + 3H_{2}O(g)[/tex]

Standard values of bond energies are as follows.

C-C = 347 kJ/mol

C-H = 414 kJ/mol

C-O = 360 kJ/mol

O-H = 464 kJ/mol

O=O = 498 kJ/mol

C=O = 799 kJ/mol

Hence, calculate the change in enthalpy of the reaction as follows.

 [tex]\Delta H_{rxn} = \sum \text{bond energy of reactants} - \sum \text{bond energy of products}[/tex]

= [5(C-H) + 1(C-C) + 1(C-O) + 1(O-H) + 3(O=O)] - [4(C=O) + 6(O-H)]

 = [tex][5 \times 414 + 1 \times 347 + 1 \times 360 + 1 \times 464 + 3 \times 498] kJ - [4 \times 799 + 6 \times 464]kJ[/tex]

       = (4735 - 5980) kJ

       = -1245 kJ

Thus, we can conclude that the enthalpy of given reaction is -1245 kJ.

The enthalpy for the combustion of ethanol, calculated using average bond energies, is -1245 kJ/mol.

Let's consider the following combustion equation.

CH₃CH₂OH(g) + 3 O₂(g) → 2 CO₂(g) + 3 H₂O(g)

Given the average bond energies, we can calculate the enthalpy of the reaction (ΔHrxn) using the following equation.

[tex]\Delta H_{rxn} = \Sigma broken\ bonds - \Sigma formed\ bonds[/tex]

The broken bonds, with their bond energies, are:

CH₃CH₂OH

  • 5 C-H (414 kJ/mol)
  • 1 C-C (347 kJ/mol)
  • 1 C-O (360 kJ/mol)
  • 1 O-H (464 kJ/mol)

O₂

  • 3 O=O (498 kJ/mol)

The formed bonds, with their bond energies, are:

CO₂

  • 4 C=O (799 kJ/mol)

H₂O

  • 6 O-H (464 kJ/mol)

The enthalpy of the reaction is:

[tex]\Delta H_{rxn} = 5\Delta H(C-H) + 1\Delta H(C-C) + 1\Delta H(C-O) + 1\Delta H(O-H)+3\Delta H(O=O)-4\Delta H(C=O)-6\Delta H(O-H)\\\\\Delta H_{rxn} = 5(414kJ/mol) + 1(347kJ/mol) + 1(360 kJ/mol) + 1(464kJ/mol)+3(498kJ/mol)-4(799kJ/mol)-6(464kJ/mol)= -1245kJ/mol[/tex]

The enthalpy for the combustion of ethanol, calculated using average bond energies, is -1245 kJ/mol.

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