Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
Enthalpy (H) is the total heat content of a system at constant pressure. It is a thermodynamic property that includes internal energy and the product of pressure and volume.
5 Must Know Facts For Your Next Test
Enthalpy change ($\Delta H$) represents the heat absorbed or released during a chemical reaction at constant pressure.
A positive $\Delta H$ indicates an endothermic process, whereas a negative $\Delta H$ indicates an exothermic process.
Standard enthalpy change of formation ($\Delta H_f^\circ$) is the enthalpy change when one mole of a compound forms from its elements in their standard states.
Hess's Law states that the total enthalpy change for a reaction is the sum of all changes, regardless of the steps taken to achieve the reaction.
Enthalpy can be measured using calorimetry by determining temperature changes in a controlled environment.
Review Questions
Related terms
Internal Energy (U): The total energy contained within a system, including both kinetic and potential energy at the molecular level.
The measurement of heat transfer during chemical reactions or physical changes using a calorimeter.
$\Delta H_f^\circ$: $\text{Standard Enthalpy Change of Formation}$: The enthalpy change when one mole of compound forms from its elements in their standard states.