Ammonium nitrate is an important fertilizer that supplies nitrogen to crops. It also can be used as an explosive to remove tree stumps from farm fields or in terrorist bombings. There are two reactions that can occur to produce the explosive effect. At lower temperatures ammonium nitrate decomposes to form dinitrogen monoxide and water vapor, but at higher temperatures it decomposes explosively to form nitrogen, water vapor, and oxygen. The reaction equations and thermodynamic parameters at 298 K are
(1) NH4NO3(s) ⇌ N2O(g) + 2 H2O(g) ΔrH° = −36.026 kJ/mol ΔrS° = 446.42 J K−1 mol−1
(2) NH4NO3(s) ⇌ N2(g) + ½ O2(g) + 2 H2O(g) ΔrH° = −118.076 kJ/mol ΔrS° = 520.749 J K−1 mol−1
a) Which of the reactions is(are) product-favored at room temperature? Which of the reactions is(are) product-favored at 1000 K? Explain briefly.
b) Is there a temperature below which one of the reactions is more product-favored and above which the other reaction is more product-favored? If there is such a temperature for these two reactions, determine what that temperature is.
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