ThermochemistryHard

Question

The standard molar enthalpies of formation of trinitrotoluene(l), CO2(g) and H2O(l) are 65, −395 and −285 kJ/mol, respectively. The density of trinitrotoluene is 1.816 g/ml. Trinitrotoluene can be used as rocket fuel, with the gases resulting from its combustion streaming out of the rocket to give the required thrust. What is the enthalpy density for the combustion reaction of trinitrotoluene?

Options

A.−28.34 MJ/L
B.−28.34 kJ/L
C.−27.30 MJ/L
D.−8.59 MJ/L

Solution

$(l) + \frac{21}{4}O_{2}(g) \rightarrow 7CO_{2}(g) + \frac{5}{2}H_{2}O(l) + \frac{3}{2}N_{2}(g) $$${\Delta H = 7 \times ( - 395) + \frac{5}{2} \times ( - 285) - (65) }{ = - 3542.5\text{ kJ/mol} }{ = - \frac{3542.5}{227} \times 1.816\text{ kJ/mol} }{ = - 28.34\text{ kJ/mol} = - 28.34\text{ MJ/L}}$$

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