Question

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.

Answer 1

Explanation:

The reaction is as follows.

       $CH_{3}CH_{2}OH(g) + 3O_{2}(g) \rightarrow 2CO_{2} + 3H_{2}O(g)$

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.

 $\Delta H_{rxn} = \sum \text{bond energy of reactants} - \sum \text{bond energy of products}$

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

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

       = (4735 - 5980) kJ

       = -1245 kJ

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