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5.88. Military Explosives Explosives called amatols are mixtures of ammonium nitrate and TNT introduced during World War I when TNT was in short supply. The mixtures can provide 30% more explosive power than TNT alone. Above 300°C, ammonium nitrate decomposes to N, O, and H,O. Write a balanced chemical reaction describing the decomposition of ammonium nitrate, and determine the standard enthalpy of reaction by using the appropriate standard enthalpies of formation from Appendix 4.

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Answer:

[tex]\large \boxed{\text{-237.0 kJ/mol}}[/tex]

Explanation:

2NH₄NO₃(s) ⟶ 2N₂(g) + O₂(g) + 4H₂O(g)

The formula for calculating the enthalpy change of a reaction by using the enthalpies of formation of reactants and products is

[tex]\Delta_{\text{r}}H^{\circ} = \sum \Delta_{\text{f}} H^{\circ} (\text{products}) - \sum\Delta_{\text{f}}H^{\circ} (\text{reactants})[/tex]

                          2NH₄NO₃(s) ⟶ 2N₂(g) + O₂(g) + 4H₂O(g)

ΔH°f/kJ·mol⁻¹:         -365.1               0            0        -241.8

[tex]\begin{array}{rcl}\Delta_{\text{r}}H^{\circ} & = & 4\times(-241.8) - 2\times(-365.1)\\& = & -967.2 + 730.2\\& = & \textbf{-237.0 kJ/mol}\\\end{array}\\\text{The enthalpy of reaction is }  \large \boxed{\textbf{-237.0 kJ/mol}}[/tex]