Heat of Formation
| Formula / Notation | ΔH°f: elements(standard state) → compound; e.g., H₂+½O₂→H₂O: −285.8 kJ/mol |
|---|---|
| Also Known As | Standard heat of formation, ΔH°f, molar enthalpy of formation, heat of formation |
What is Heat of Formation?
The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states at 298 K and 1 atm. Standard heats of formation for elements in their standard states are zero by definition. Used in Hess's law calculations.
Formula & Notation
Other Names / Synonyms: Standard heat of formation, ΔH°f, molar enthalpy of formation, heat of formation
Properties & Characteristics
Uses & Applications
Safety Information
Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.
Key Facts
Frequently Asked Questions
The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states at 298 K and 1 atm. Standard heats of formation for elements in their standard states are zero by definition. Used in Hess's law calculations.
Standard enthalpies of formation are used to calculate heats of any reaction via Hess's law, to compare stability of isomers, to design fuels and energetic materials, and in industrial process design. They are tabulated in the NIST WebBook and CODATA databases for thousands of compounds.
Compounds with very negative ΔH°f (stable products) drive reactions exothermically when formed from reactive elements. Conversely, compounds with positive ΔH°f (e.g., HI, N₂H₄) are thermodynamically unstable relative to elements and may decompose exothermically or explosively.
The formula or notation for Heat of Formation is: ΔH°f: elements(standard state) → compound; e.g., H₂+½O₂→H₂O: −285.8 kJ/mol