question_answer

\[\Delta E{}^\circ \] of combustion of isobutylene is \[-x\,kJ mol{{\,}^{-}}^{1}\]. The value of \[\Delta H{}^\circ \] is

A)  \[=\Delta \,E{}^\circ \]             

B)  \[>\Delta \,E{}^\circ \]

C)  \[=zero\]                      

D)  \[<\Delta \,E{}^\circ \]

Correct Answer: B

Solution :

We know that \[\Delta H{}^\circ =\Delta E{}^\circ +\Delta {{n}_{g}}RT\] For the reaction \[\Delta {{n}_{g}}=4-7=-\,3\] \[\therefore \,\,\,\,\,\,\,\,\,\Delta H{}^\circ  = \Delta E{}^\circ -\Delta n{{\,}_{g}}RT\,\, \left[ \because  \,\Delta {{n}_{g}} = negative \right]\] i.e.,     \[\Delta H{}^\circ <\Delta E{}^\circ \]