The concept of standard enthalpy of formation and standard state for an element and compound has to be discussed.
Standard enthalpy of formation (): The standard enthalpy of formation is defined as the change in enthalpy when one mole of a substance in the standard state (1atm of pressure and 298.15 K) is formed from its pure elements under the same conditions.
Standard state: Standard state precisely defined as reference state. It is a common reference point that can used to compare thermodynamic properties.
Hess’s law: Hess's law states that the change of enthalpy in a chemical reaction (i.e. the heat of reaction at constant pressure) is independent of the pathway between the initial and final states.
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