Question

A terrorist has decided to use nitroglycerin (NG) in a firearm as a propellant. He weighs out 1.5g of NG and his bullet weighs 200grains. If we assume combustion goes to completion (i.e. 100%) and that the conversion of chemical energy to kinetic energy is 60% efficient (i.e. energy transferred to the bullet), how fast will the bullet be moving?

Answer 1

mass of NG = 1.5 g

moles of NG = mass NG / molar mass NG

moles of NG = (1.5 g) / (227.0865 g/mol)

moles of NG = 6.6054 x 10^-3 mol

Enthalpy of combustion of NG = -1529 kJ/mol

Heat released = (Enthalpy of combustion of NG) * (moles of NG)

Heat released = (-1529 kJ/mol) * (6.6054 x 10^-3 mol)

Heat released = 10.1 kJ

Energy transferred = 60 % heat released

Energy transferred = (60 %) * (10.1 kJ)

Energy transferred = (0.60) * (10.1 kJ)

Energy transferred = 6.06 kJ

Kinetic energy of bullet = 6.06 kJ = 6.06 x 10³ J

mass of bullet = 200 g = 0.200 kg

also, kinetic energy = 0.5 * m * v²

where m = mass = 0.200 kg

v = velocity of bullet

v² = kinetic energy / (0.5 * m)

v² = 6.06 x 10³ J / (0.5 * 0.200 kg)

v² = 60600 m²/s²

v =

v = 246.2 m/s