JEE Main & Advanced Chemistry Thermodynamics / रासायनिक उष्मागतिकी Sample Paper Topic Test - Thermo Chemistry (Thermodynamics)

The enthalpy of combustion of \[{{H}_{2}}(g),\] to give\[{{H}_{2}}(g)\] is \[-249\text{ }kJ\text{ }mo{{l}^{-1}}\] and bond enthalpies of \[H-H\] and \[O=O\] are \[433\text{ }kJ\text{ }mo{{l}^{-1}}\] and \[492\text{ }kJ\text{ }mo{{l}^{-1}}\] respectively. The bond enthalpy of \[O-H\] is

A) \[464\text{ }kJ\text{ }mo{{l}^{-1}}\]

B) \[-464\text{ }kJ\text{ }mo{{l}^{-1}}\]

C) \[232\text{ }kJ\text{ }mo{{l}^{-1}}\]

D) \[-232\text{ }kJ\text{ }mo{{l}^{-1}}\]

Correct Answer: A

Solution :

[a] \[{{H}_{2}}(g)+\frac{1}{2}{{O}_{2}}(g)\to {{H}_{2}}O(g)?h=-249\]

Let the bond enthalpy of \[O-H\] is x. Then \[\Delta H=\sum B.E.\] of reactant \[-\sum B.E.\] of product

\[-249=433+\frac{1}{2}\times 492-2x\]

\[\Rightarrow \] \[x=46\,kJ\,mo{{l}^{-1}}\]