Which of the following best describes bond dissociation energy?

• A. The energy required to ionize one mole of atoms in the gas phase.
• B. The energy required to break one mole of a specific bond in a gaseous molecule, forming separated atoms in the gas phase.
• C. The energy released when two atoms form a chemical bond in the solid state.
• D. The energy needed to convert a liquid into a gas at its boiling point.

Answer: (B)

Verified step by step guidance

1. Understand that bond dissociation energy (BDE) refers to the energy involved in breaking chemical bonds, specifically in molecules in the gas phase.
2. Recall that BDE is defined as the energy required to break one mole of a particular type of bond in a gaseous molecule, resulting in separated atoms also in the gas phase.
3. Differentiate BDE from other energy concepts: ionization energy involves removing electrons from atoms, not breaking bonds; energy released when bonds form is bond formation energy, which is the opposite process; and energy to convert liquid to gas is related to phase changes, not bond breaking.
4. Recognize that BDE is always a positive value because energy must be supplied to break bonds, overcoming the attractive forces holding atoms together.
5. Summarize that the best description of bond dissociation energy is the energy required to break one mole of a specific bond in a gaseous molecule, forming separated atoms in the gas phase.