What is the standard enthalpy of formation denoted as?

The standard enthalpy of formation is denoted as Δ_fH® (where the superscript circle indicates standard conditions). This term specifically refers to the change in enthalpy when one mole of a compound is formed from its elements in their standard states. The standard state typically means the most stable form of the element at 1 bar of pressure and a specified temperature, usually 25 degrees Celsius.

This notation is crucial as it differentiates the standard enthalpy of formation from other thermodynamic quantities. For example, Δ_rH refers to the change in enthalpy for a reaction at any specified conditions, while Δ_cH indicates the enthalpy change during combustion. Thus, the precise notation of Δ_fH® captures the specific context of forming compounds from their elemental states under standard conditions, making it the correct representation for standard enthalpy of formation.