Free Bond Energy MCQs with Answers

1. Bond energy is defined as the energy

• A. released when a bond is formed between two ions
• B. required to melt one mole of a covalent solid
• C. required to break one mole of a particular bond in the gaseous state
• D. stored in the nucleus of an atom

Explanation: Because bond breaking is always endothermic, bond energy values are positive, and the same amount is released when the bond re-forms. The gaseous state is specified so that intermolecular forces do not contribute to the measurement. Values quoted in data books are averages taken across many compounds, which is why calculations using them give approximate results.

2. Among the carbon to carbon bonds, the order of bond energy is

• A. single greater than double greater than triple
• B. all three are equal
• C. double greater than triple greater than single
• D. triple greater than double greater than single

Explanation: More shared pairs mean a greater attraction between the nuclei and the bonding electrons, so the triple bond is the strongest and also the shortest at 0.120 nm, against 0.154 nm for a single bond. Bond energy and bond length always move in opposite directions. Note that a triple bond is not three times as strong as a single one, because the two pi bonds are weaker than the sigma bond.

3. A reaction is exothermic overall when

• A. the energy released in forming new bonds exceeds the energy absorbed in breaking old ones
• B. the energy absorbed in breaking bonds exceeds the energy released in forming them
• C. no bonds are broken
• D. the products are gases

Explanation: Breaking bonds always costs energy and forming them always releases it, so the sign of the overall enthalpy change is decided by which total is larger. This is the basis of calculating an approximate enthalpy change from tabulated bond energies. Combustion is strongly exothermic because the very strong bonds in carbon dioxide and water release more than was spent breaking the fuel apart.

4. Bond length decreases in the order

• A. single, double, triple
• B. triple, double, single
• C. double, single, triple
• D. all are equal

Explanation: More shared pairs pull the nuclei closer, so a triple bond is shorter than a double and a double shorter than a single, with carbon to carbon lengths of about 0.120, 0.134 and 0.154 nm respectively. Bond energy runs the opposite way, rising as the bond shortens. Bond order, length and strength are always linked in this pattern.

5. The strength of a covalent bond generally increases as

• A. the bond length increases
• B. the bond length decreases and the bond order rises
• C. the atoms become larger
• D. the electronegativity difference falls to zero

Explanation: Shorter bonds hold the nuclei closer to the shared electrons, so more energy is needed to separate them, and each extra shared pair shortens the bond further. This is why the carbon to carbon triple bond is both the shortest and the strongest of the three. Larger atoms form longer and therefore weaker bonds, which is why bond strength falls down a group.