The enthalpy of combustion of H2(g) at 298 K to give H2O(g) is -249 kJ mol−1 and bond enthalpies of H-H and O-O are 433 kJ mol−1 and 492 kJ mol−1 respectively. The bond enthalpy of O-H is
A
464kJmol−1
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B
−464kJmol−1
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C
232kJmol−1
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D
−232kJmol−1
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Solution
The correct option is A464kJmol−1 We have Given - ϵH−H=433kJmol−1 & ϵO=O=492kJmol−1 Hence, ϵH−H+12ϵO=O−2ϵO−H=(433+12×492)kJmol−−2ϵO−H=−249kJmol−1 Hence , ϵO−H=464kJmol−1