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Most Important Selected Qs for JEE AdvancedChemistryThermodynamics (C)

Paragraph: Consider the following data (all values in kJ mol ⁻¹ at 25^ C ) and answer the questions that follow. (i) Enthalpy of polymerisation of ethene =-72 (ii) Enthalpy of formation of benzene (I) =49 (iii) Enthalpy of vaporisation of benzene ( I )=30 (iv) Resonance energy of benzene =-152 (v) Heat of formation of gaseous atoms from the element in their standard state: H =218, C =715 and average C - H bond energy

Options

  1. A615.33 ~kJ ~mol ⁻¹
  2. B513.00 ~kJ ~mol ⁻¹
  3. C567.46 kJ mol
  4. D650.30 ~kJ ~mol ⁻¹

Correct answer

A. 615.33 ~kJ ~mol ⁻¹

Step-by-step solution

Let B.E. of C=C be x and B . E . of C-C be y n ( CH ₂= CH ₂ ) ( CH ₂- CH ₂⁻ )_ n x-2 y=-72 ...(i) aligned & H_r= H_f (C₆ H₆, I )+ H_ vap (C₆ H₆, I )-R E & =49+30-(-152)=231 & 231=6 715+6 218-3(x+y)-6 415 aligned x+y=959 On solving (i) and (ii) we get x=615.33 and y=343.67

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