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JIPMER2017ChemistryThermodynamics (C)

The energy released when 6 moles of octane is burnt in air will be [Given, H_f^ for CO ₂(g) , H ₂ O ( g ) and C ₈ H ₁₈( l ) , respectively are -490 , -240 and +160 ~J / mol ]

Options

  1. A-37.4 ~kJ
  2. B-20 ~kJ
  3. C-6.2 ~kJ
  4. D-35.5 ~kJ

Correct answer

D. -35.5 ~kJ

Step-by-step solution

aligned C + O ₂ CO ₂ ; H=-490 ~J ....(i) H ₂+ 1 2 O ₂ H ₂ O ; H=-240 ~J ....(ii) 8 C +9 H ₂ C ₈ H ₁₈ ; H=+160 ~J ....(iii) aligned On applying, 8 x Eq. (i) +9 x Eq. (ii)-Eq. (iii), we get aligned & C ₈ H ₁₈+ 25 2 O ₂ 8 CO ₂+9 H ₂ O & H_R^0=[8 (-490)]+[9 (-240)]+160 aligned =-5920 ~J ~mol ⁻¹ Hence, energy exchange when 6 moles of octane is burnt in air =-5920 6=-35520 ~J =-35.5 kJ

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