What is meant by the term average bond enthalpy? Why is there difference in bond enthalpy of O−H bond in ethanol (C2H5OH) and water?
What is meant by the term average bond enthalpy? Why is there difference in bond enthalpy of O−H bond in ethanol (C2H5OH) and water?
Definition of average bond enthalpy
Bond enthalpy is the amount of energy required to break one mole of bonds of a particular type between two atoms in gaseous state.
Average Bond Enthalpy is obtained by dividing total bond dissociation enthalpy by the number of bonds broken. All the identical bonds in a molecule do not have the same bond enthalpies, for example water.
H2O(g)→H(g)+OH(g);
ΔαH1=502kJmol−1
OH(g)→H(g)+O(g);
ΔbH2=427kJmol−1
Average bond enthaply
=502+4272=464.5kJmol−1
Comparing bond enthalpies of O—H bond in ethanol and water
There is a difference in bond enthalpy of
O−H bond in ethanol and water. It is so because of the difference in electronegativities of the atoms to which oxygen is further linked i.e., hydrogen in water and carbon in ethanol.
Since electronegativity difference in hydrogen and oxygen is different than that in carbon and oxygen, O−H bond in water has different bond enthalpy than in ethanol
Definition of average bond enthalpy
Bond enthalpy is the amount of energy required to break one mole of bonds of a particular type between two atoms in gaseous state.
Average Bond Enthalpy is obtained by dividing total bond dissociation enthalpy by the number of bonds broken. All the identical bonds in a molecule do not have the same bond enthalpies, for example water.
H2O(g)→H(g)+OH(g);
ΔαH1=502kJmol−1
OH(g)→H(g)+O(g);
ΔbH2=427kJmol−1
Average bond enthaply
=502+4272=464.5kJmol−1
Comparing bond enthalpies of O—H bond in ethanol and water
There is a difference in bond enthalpy of
O−H bond in ethanol and water. It is so because of the difference in electronegativities of the atoms to which oxygen is further linked i.e., hydrogen in water and carbon in ethanol.
Since electronegativity difference in hydrogen and oxygen is different than that in carbon and oxygen, O−H bond in water has different bond enthalpy than in ethanol
