A chemical engineer uses a table of average bond energies to calculate the molar enthalpy change for the synthesis of gaseous hydrazine, which is used as a rocket propellant:
N2(g)+2H2(g)→N2H4(g) \text{N}_2(\text{g}) + 2\text{H}_2(\text{g}) \rightarrow \text{N}_2\text{H}_4(\text{g}) N2(g)+2H2(g)→N2H4(g)The average bond energies are shown in the table below:
| Bond | Average bond energy in kJ/mol\text{kJ/mol}kJ/mol |
|---|---|
| N≡N\text{N}\equiv\text{N}N≡N | 944 |
| H−H\text{H}-\text{H}H−H | 436 |
| N−N\text{N}-\text{N}N−N | 163 |
| N−H\text{N}-\text{H}N−H | 388 |
In this reaction:
Calculate the energy taken in (in kJ\text{kJ}kJ) when the bonds in the reactants are broken.
Calculate the energy given out (in kJ\text{kJ}kJ) when the bonds in the products are formed.
Use your answers to (i) and (ii) to calculate the molar enthalpy change, ΔH\Delta HΔH (in kJ/mol\text{kJ/mol}kJ/mol), for the synthesis of hydrazine.
