GATE 2023 CY – Question 58

Inorganic Chemistry · Main Group Elements: Shapes and structures of molecules using VSEPR postulates, Hydrides, halides, oxides, oxoacids, nitrides, sulfides - shapes and reactivity. Structure and bonding of boranes, carboranes, silicones, silicates, boron nitride, borazine and phosphazenes: electron counting in polyhedral boranes, isolobal analogy. Allotropes of carbon, phosphorus and sulfur. Industrial synthesis of compounds of main group elements such as NH3, H2SO4 and HNO3. Chemistry of noble gases and interhalogen compounds. Acid-base concepts and principles (Lewis, Brønsted, HSAB and acid-base catalysis). · 2 marks · Numerical answer

The enthalpy change for the exothermic reaction between $BeI_2$ and $HgF_2$ is ______ kJ/mol (nearest integer). Bond dissociation energies (kJ/mol): Be–F 632, Be–I 289, Hg–F 268, Hg–I 145.

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Correct answer: -440 to -440

Explanation

Break two Be–I and two Hg–F bonds: energy=2(289)+2(268)=1114 kJ/mol. Form two Be–F and two Hg–I bonds, releasing 2(632)+2(145)=1554 kJ/mol. ΔH=broken−formed=**−440 kJ/mol**, consistent with the stated exothermic reaction.