Which bond in each pair has the higher bond dissociation energy?

a.

b.

The amount of energy that is essential to break a chemical bond is termed the bond dissociation energy.

Size of the bonded atoms: As the size of the bonded atom increases the bond length increases and the bond strength decreases thereby decreasing the bond dissociation energy.

The number of electrons involved in bonding: As the number of electrons shared between two atoms (i.e., the number of bonds between two atoms) increases the bond strength increases and thus the bond dissociation energy also increases.

a.

The compound with higher bond dissociation energy

The first compound consists of a carbon-oxygen (C-O) and the second compound consists of a carbon-sulfur (C-S) bond.

Since sulfur is bigger in size than oxygen the carbon-sulfur (C-S) bond is weaker compared to the carbon-oxygen (C-O) bond.

Therefore, the carbon-oxygen (C-O) bond has higher bond dissociation energy than the carbon-sulfur (C-S) bond.

b.

Compound with higher bond dissociation energy

The first compound consists of a carbon-oxygen double bond while the second one has a carbon-oxygen single bond.

Since a double bond has higher bond strength than a single bond, the carbon-oxygen double bond (C=O) has higher bond dissociation energy than the carbon-oxygen single bond (C-O).