Question

using the appropriate bond energies, calculate the heat of reaction (delta h) for the following reaction:

\begin{array}{c} \begin{array}{c} \begin{array}{c} \text{h} \\ \text{i} \\ \text{h}-\text{c}-\text{h} \\ \text{i} \\ \text{h} end{array} end{array} + 20 = 0
ightarrow 0 = \text{c} = 0 + 20-\text{h} end{array}

you can find a table of bond energies by using the data button on the aleks toolbar.

round your answer to the nearest (mathrm{kj} / mathrm{mol}).

note: for clarity, all lone pairs have been omitted from the molecular structures.

\frac{mathrm{kj}}{mathrm{mol}}

Explanation:

Step1: Calculate energy required to break bonds

• Methane (\(CH_4\)) has \(4\) \(C - H\) bonds. Bond energy of \(C - H\) is \(413\space kJ/mol\). So energy for \(CH_4\) is \(4\times413\space kJ/mol\).
• Oxygen (\(O_2\)) has \(2\) \(O = O\) bonds. Bond energy of \(O = O\) is \(498\space kJ/mol\). So energy for \(2O_2\) is \(2\times498\space kJ/mol\).
• Total energy to break bonds: \(4\times413+2\times498=(1652 + 996)\space kJ/mol=2648\space kJ/mol\)

Step2: Calculate energy released when bonds form

• Carbon dioxide (\(CO_2\)) has \(2\) \(C = O\) bonds. Bond energy of \(C = O\) is \(799\space kJ/mol\). So energy for \(CO_2\) is \(2\times799\space kJ/mol\).
• Water (\(H_2O\)) has \(2\) \(O - H\) bonds. For \(2H_2O\), there are \(4\) \(O - H\) bonds. Bond energy of \(O - H\) is \(467\space kJ/mol\). So energy for \(2H_2O\) is \(4\times467\space kJ/mol\).
• Total energy released: \(2\times799+4\times467=(1598+1868)\space kJ/mol = 3466\space kJ/mol\)

Step3: Calculate \(\Delta H\)

Using the formula \(\Delta H=\text{Energy to break bonds}-\text{Energy released when bonds form}\)
\(\Delta H = 2648-3466=- 818\space kJ/mol\)

Answer:

\(-818\space kJ/mol\)