What is bond enthalpy?

Bond enthalpy, often referred to as bond dissociation energy, specifically quantifies the energy required to break a bond in a mole of gaseous molecules. When a bond between two atoms is broken, energy must be supplied to overcome the attractive forces holding the atoms together. This process is measured in kilojoules per mole and represents the average energy needed to break that particular type of bond in a molecule across many instances.

In this context, energy changes are only considered when the substance is in the gas phase for bond enthalpy measurements. This specificity is crucial, as different phases (solid, liquid, gas) can involve different interactions and energies.

The other options refer to different concepts. For instance, the total energy required to complete a chemical reaction encompasses not only the energy required to break bonds but also includes energy associated with bond formation and any other energy changes that may occur during the reaction. The energy associated with changing the state of matter refers to phase transitions, such as melting or boiling, which do not involve breaking or forming chemical bonds directly. The energy needed to form a bond between two atoms is a related concept but contextually focuses on bond formation rather than the energy required to break an existing bond, which is what bond enthal