If enthalpy of atomisation for $\mathrm{Br}_{2}(\mathrm{~A})$ is $\mathrm{x}$ $\mathrm{kJ/mol}$ and bond enthalpy for $\mathrm{Br}_{2}$ is $\mathrm{y}$ $\mathrm{kJ/mol}$, the relation between them:

JEE Main · 2020 · 09 Jan 2020 · Shift 1 · Chemical Thermodynamics

If enthalpy of atomisation for

Br_{2} (A)

x

kJ/mol

and bond enthalpy for

Br_{2}

y

kJ/mol

, the relation between them:

Answer: (B)

Atomising

B r_{2}

means taking the liquid all the way to free gaseous atoms,

B r_{2} (l) \to 2Br (g)

, which requires first vaporising the liquid and then breaking the bond, so

Δ H_{atom} = Δ H_{vap} + Δ H_{bond}

. The bond enthalpy

y

accounts only for breaking the bond of the gaseous molecule, so the atomisation enthalpy

x

exceeds it by the vaporisation term, that is

x > y

JEE Main · 2020 · 09 Jan 2020 · Shift 1 · Single correct option