One chemical reaction used to propel spacecraft is the combustion of hydrazine. The balanced symbol equation for this reaction is:
N2H4+O2→N2+2H2O\text{N}_2\text{H}_4 + \text{O}_2 \rightarrow \text{N}_2 + 2\text{H}_2\text{O}N2H4+O2→N2+2H2O
A molecule of hydrazine (N2H4\text{N}_2\text{H}_4N2H4) contains four N−H\text{N}-\text{H}N−H bonds and one N−N\text{N}-\text{N}N−N bond. A molecule of oxygen (O2\text{O}_2O2) contains one O=O\text{O}=\text{O}O=O bond. A molecule of nitrogen (N2\text{N}_2N2) contains one N≡N\text{N}\equiv\text{N}N≡N bond. A molecule of water (H2O\text{H}_2\text{O}H2O) contains two O−H\text{O}-\text{H}O−H bonds.
The table below shows the average bond energies:
| Bond | Bond energy (kJ/mol) |
|---|---|
| N−H\text{N}-\text{H}N−H | 391 |
| N−N\text{N}-\text{N}N−N | 158 |
| O=O\text{O}=\text{O}O=O | 498 |
| N≡N\text{N}\equiv\text{N}N≡N | 945 |
| O−H\text{O}-\text{H}O−H | 464 |
Calculate the energy transferred when all the bonds form in the products.
The energy transferred when all the bonds break in the reactants is 2220 kJ/mol2220\text{ kJ/mol}2220 kJ/mol. Use your answer to part (a) to calculate the overall energy change for this reaction.