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AIIMS2004ChemistryThermodynamics (C)

How much energy is released when 6 moles of octane is burnt in air? Given H_f^ for CO _ 2(g) , H ₂ O _ ( g ) and C ₈ H _ 18(l) respectively are -490,-240 and +160 ~kJ / mol .

Options

  1. A-6.2 ~kJ
  2. B-37.4 ~kJ
  3. C-35.5 ~kJ
  4. D-20.0 ~kJ

Correct answer

B. -37.4 ~kJ

Step-by-step solution

array r C + O ₂ CO ₂ ; H_f^ =-490 ~kJ / mol 8 H ₂+ 1 2 O ₂ H ₂ O ; H_f^ =-240 ~kJ / mol 9 8 C +18 H C ₈ H ₁₈ ; H_f^ =+160 ~kJ / mol 8 C +8 O ₂+9 H ₂+ 9 2 O ₂-8 C -18 H 8 CO ₂+9 H ₂ O - C ₈ H ₁₈ H_f^ =-3920-2160-160 C ₈ H ₁₈+ 25 2 O ₂ 8 CO ₂+9 H ₂ O ; H^ =-6240 ~kJ / mol H^ for 6 moles of octane =-6240 6=-37440 ~kJ / mol . array

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