Q23 / 91 · KVPY 2018 (SB/SX) · Chemistry

Nitroglycerine MW=227.1 detonates according to the following equations,

2C3H5NO33l⟶3 N2g+12O2g+6CO2g+5H2Og

The standard molar enthalpies of formation, ΔHf° for all the compounds are given below.

ΔHf°C3H5NO33=-364 kJ/mol
ΔHf°CO2g=-393.5 kJ/mol
ΔHf°H2Og=-241.8 kJ/mol
ΔHf°N2g=0 kJ/mol
ΔHf°O2g=0 kJ/mol

The enthalpy change when 10 g of nitroglycerine is detonated is

  • A
    -100.5 kJ/mol
  • Correct answer
    B
    -62.5 kJ/mol
  • C
    -80.3 kJ/mol
  • D
    -74.9 kJ/mol

Solution

FigureFigure

ΣHReaction°=ΣHfP°-ΣHf(R)°

ΔHReaction°=3×0+12×0+6×-393.5+5×-241.8-2×-364

=-2361-1209+728

=-2842 kJ/mol

For 2 moles of nitroglycerine enthalpy
-2842 kJ/mol

∴ For 1 mole of nitroglycerine enthalpy
=-28422=-1421 kJ/mol

227.1 g of C3H5NO33 has enthalpy -1421 kJ/mol.

∴10 g of C3H5NO33 has enthalpy

=-1421227.1×10

=-62.5 kJ/mol

Hence, the correct answer is option: 'B'.

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