What is the enthalpy of sublimation?

The enthalpy of sublimation is defined as the amount of energy required to transform a substance from a solid state directly into a gaseous state, bypassing the liquid phase. This process involves breaking the intermolecular forces that hold the solid structure together, which requires a specific amount of energy input.

In the context of the enthalpy of sublimation, option B correctly describes this process as the difference in enthalpy per mole between the gaseous and solid states. It captures the essential aspect of sublimation by highlighting that it is the energy change associated with moving from the solid phase to the gaseous phase. This choice effectively encompasses the heat needed to make this transition, which is pivotal for understanding phase changes in substances.

In contrast, the other options focus on different thermodynamic processes. The first option pertains to melting (solid to liquid), the third to deposition (gas to solid), and the fourth relates to mixing liquids. These processes involve different types of energy changes and are not relevant to sublimation specifically. Thus, option B stands out as the correct choice for defining the enthalpy of sublimation within the context of physical chemistry.