What is the equation for the relationship of standard enthalpy change concerning phases?

The relationship between the enthalpy changes for different phases of a substance can be expressed through the concept of the enthalpy of fusion (Δ_fusH), enthalpy of vaporization (Δ_vapH), and enthalpy of sublimation (Δ_subH).

Sublimation refers to the direct transition of a substance from solid to gas without passing through the liquid phase. Therefore, the enthalpy change associated with sublimation is the sum of the enthalpy change required to first melt the solid (enthalpy of fusion) and then the enthalpy change required to vaporize the resulting liquid (enthalpy of vaporization).

This gives us the equation: Δ_subH = Δ_fusH + Δ_vapH.

This equation encapsulates the idea that when a solid is converted directly to a gas, the energy associated with melting and subsequently vaporizing the liquid must be taken into account.

Understanding this relationship is critical in thermochemistry, as it helps predict how much energy will be needed for phase transitions under standard conditions. Additionally, applying this knowledge can help solve problems involving different phase transitions and their respective enthalpy changes.