MEDIUMMCQ SINGLEIChO (Chemistry Olympiad)Physical ChemistryThermodynamics and ThermochemistryPrevious Year Questions

Bond dissociation enthalpy of H₂ Cl₂, and HCl are 434, 242 and 431 kJ mol respectively. Enthalpy of formation of HCl is (2008)

A.–93 kJ mol–1✓ Correct

B.245 kJ mol–1

C.93 kJ mol–1

D.–245 kJ mol–1

Explanation

H₂ + Cl₂ → 2 HCl reaction reactants products H H Cl Cl (H Cl) reaction H (B.E) (B.E) [(B.E) (B.E) ] [2B.E ] 434 242 (431) 2 H 186kJ x Hence, enthalpy of formation of HCl –1 186 93kJ mol 2

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