Chemistry - Thermochemistry Question with Solution | TestHub
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:
Answer:
Solution:
The combustion of trinitrotoluene (TNT) can be represented by the following balanced chemical equation:
C7H5N3O6(l) + 21/4O2(g) tarrow 7CO2(g) + 5/2H2O(l) + 3/2N2(g)
The standard enthalpy of combustion, Δ Hc, is calculated as:
Δ Hc = [7(-395) + 2.5(-285)] - [65] = -2765 - 712.5 - 65 = -3542.5 kJ/mol
The molar mass of TNT is 227 g/mol. Given a density of 1816 g/L, the moles per liter can be calculated as:
Moles per liter = (1816 g/L)/(227 g/mol) = 8 mol/L
The enthalpy density is then:
Enthalpy density = -3542.5 kJ/mol × 8 mol/L = -28340 kJ/L = -28.34 MJ/L
This corresponds to option (a).
