What is AHf?

AHf, or standard enthalpy of formation, is a measure of the heat change that occurs when one mole of a compound is formed from its elements in their standard states at a specified temperature, usually 25°C (298 K). It is expressed in kilojoules per mole (kJ/mol) and is a crucial concept in thermodynamics and chemistry for predicting the energy changes in chemical reactions. The standard enthalpy of formation of elements in their most stable form is defined as zero.