Question
Give difference between bond dissociation enthalpy and average bond dissociation enthalpy. Explain.
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Answer
Bond dissociation enthalpy : The enthalpy change in breaking of all the bonds present in one mole of gaseous covalent diatomic molecule to form a gaseous product is called bond dissociation enthalpy.
Example : $H _2(g) \rightarrow 2 H ( g ) \Delta_{ H - H }=435.0 kJ mol ^{-1}$
Average bond enthalpy : The average of total energy required to break all bonds of same type present in polyatomic molecules is called average bond enthalpy.
Avg. bond enthalpy of $C - H$ bond in $CH _4$
$=\frac{\text { Total energy required to break all four } C - H \text { bond }}{4}$
Example : $H _2(g) \rightarrow 2 H ( g ) \Delta_{ H - H }=435.0 kJ mol ^{-1}$
Average bond enthalpy : The average of total energy required to break all bonds of same type present in polyatomic molecules is called average bond enthalpy.
Avg. bond enthalpy of $C - H$ bond in $CH _4$
$=\frac{\text { Total energy required to break all four } C - H \text { bond }}{4}$
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