JEE Main · 2020 · Shift-IeasyTHERMO-122

If enthalpy of atomization for Br2(l) is x\,kJ/mol and bond enthalpy for Br2 is y\,kJ/mol, the relation between them:

Thermodynamics · Class 11 · JEE Main Previous Year Question

Question

If enthalpy of atomization for Br2(l)\text{Br}_2(l) is x kJ/molx\,\text{kJ/mol} and bond enthalpy for Br2\text{Br}_2 is y kJ/moly\,\text{kJ/mol}, the relation between them:

Options
  1. a

    x=yx=y

  2. b

    does not exist

  3. c

    x>yx>y

    ✓
  4. d

    x<yx<y

Correct Answerc

x>yx>y

Detailed Solution

🧠 Atomization from liquid adds vaporization on top of bond dissociation Bond enthalpy is defined for gas-phase molecules. Atomization of \ceBr2(l)\ce{Br2(l)} requires first vaporizing the liquid, then breaking the bond — two steps, both endothermic.

x=ΔHvap+yx = \Delta H_{\text{vap}} + y

Since ΔHvap>0\Delta H_{\text{vap}} > 0, it follows that x>yx > y.

Answer: (c) x>y\boxed{\text{Answer: (c) } x > y}

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