The standard molar enthalpies of formation of nitroglycerine(l), CO 2 (g) and H 2 O(l) are -364, -395 and -285 kJ/mol, respectively. The density of nitroglycerine is 1.60 g/ml. Nitroglycerine (C 3 H 5

Question

The standard molar enthalpies of formation of nitroglycerine(l), CO 2 (g) and H 2 O(l) are -364, -395 and -285 kJ/mol, respectively. The density of nitroglycerine is 1.60 g/ml. Nitroglycerine (C 3 H 5 N 3 O 9 ) can be used as a rocket propellant, with the gases from its decomposition streaming out to give thrust. What is the enthalpy density for the decomposition (oxidation) reaction of nitroglycerine?

TestHub · Accepted Answer

4C 3 H 5 N 3 O 9 (l) → 12CO 2 (g) + 10H 2 O(l) + 6N 2 (g) + O 2 (g). Per 4 mol: ΔH = [12(-395) + 10(-285)] - 4(-364) = -7590 + 1456 = -6134 kJ, i.e. -1533.5 kJ/mol. Molar mass = 227 g/mol, so moles per litre = 1600/227 = 7.05. Enthalpy density = -1533.5 × 7.05 = -10,810 kJ/l ≈ -10.81 MJ/l. This is option (c).

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