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NEETChemistryThermodynamics (C)

What is the value of ( H - U ) for the complete combustion of 1 mole of liquid benzene ( C₆H₆ ) at temperature T ?

Options

  1. A-1.5 RT
  2. B+1.5 RT
  3. C-2.5 RT
  4. D+2.5 RT

Correct answer

A. -1.5 RT

Step-by-step solution

The balanced chemical equation for the complete combustion of 1 mole of liquid benzene is: C₆H₆(l) + 15 2 O₂(g) 6CO₂(g) + 3H₂O(l) The change in the number of moles of gaseous species ( n_g ) is calculated as: n_g = moles of gaseous products - moles of gaseous reactants n_g = 6 - 15 2 = 6 - 7.5 = -1.5 From the relation H = U + n_g RT , we get: H - U = n_g RT H - U = -1.5 RT Treating H₂O as a gas leads to the incorrect value of +1.5 RT , and treating benzene as a gas leads to the incorrect value of -2.5 RT . Answer:

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