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KCET2021ChemistryThermodynamics (C)

Bond enthalpies of A₂, B₂ and A B are in the ratio 2: 1: 2 . If bond enthalpy of formation of A B is -100 ~kJ ~mol ⁻¹ . The bond enthalpy of B₂ is

Options

  1. A100 ~kJ ~mol ⁻¹
  2. B50 ~kJ ~mol ⁻¹
  3. C200 ~kJ ~mol ⁻¹
  4. D150 ~kJ ~mol ⁻¹

Correct answer

C. 200 ~kJ ~mol ⁻¹

Step-by-step solution

Given, ( BE )_ A₂ :( BE )_ B₂ :( BE )_ A B =2: 1: 2 where, B E= Bond enthalpy ( H_ f )_ A B =-100 ~kJ Let the BE of A₂, B₂ and A B be 2 x, x and 2 x respectively. As we know, _ f H^ = _ diss H_ R ^ - _ diss H_ P ^ where, _ diss H^ = Enthalpy of dissociation aligned 1 2 A₂ &+ 1 2 B₂ A B -100 &= ( 1 2 2 x+ 1 2 x )-x x &=200 aligned Bond enthalpy of B₂ is 200 ~kJ ~mol ⁻¹ .

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