enthalpy

American  

[en-thal-pee, en-thal-] / ˈɛn θæl pi, ɛnˈθæl- /

noun

Thermodynamics.

• enthalpies
  plural

1. a quantity associated with a thermodynamic system, expressed as the internal energy of a system plus the product of the pressure and volume of the system, having the property that during an isobaric process, the change in the quantity is equal to the heat transferred during the process. H

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enthalpy British  

/ ˈɛnθəlpɪ, ɛnˈθæl- /

noun

1.  H.  Also called: heat content.   total heat.  a thermodynamic property of a system equal to the sum of its internal energy and the product of its pressure and volume

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enthalpy Scientific  

/ ĕn′thăl′pē /

1. A partial measure of the internal energy of a system. Enthalpy cannot be directly measured, but changes in it can be. If an outside pressure on a system is held constant, a change in enthalpy entails a change in the system's internal energy, plus a change in the system's volume (meaning the system exchanges energy with the outside world). For example, in endothermic chemical reactions, the change in enthalpy is the amount of energy absorbed by the reaction; in exothermic reactions, it is the amount given off.

2. See also thermodynamics

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Other Word Forms

Noun Inflected Forms

• enthalpies
  plural

Etymology

Origin of enthalpy

1925–30; < Greek enthálp ( ein ) to warm in ( en- en- ² + thálpein to warm) + -y ³

Compare meaning

How does enthalpy compare to similar and commonly confused words? Explore the most common comparisons:

• enthalpy vs. internal energy

Example Sentences

See Examples For:

enthalpy enthalpies

This edge becomes an acceleration hotspot because pressure falls rapidly there while enthalpy density remains low.

From Science Daily ● Aug. 3, 2026

"But to predict new ceramic recipes with other transition metals, we had to address the enthalpy."

From Science Daily ● Jan. 3, 2024

To better understand the concepts of entropy and enthalpy in this application, think of a 10-year-old trying to construct a doghouse out of a giant pile of Legos.

From Science Daily ● Jan. 3, 2024

The heat given off when you operate a Bunsen burner is equal to the enthalpy change of the methane combustion reaction that takes place, since it occurs at the essentially constant pressure of the atmosphere.

From Textbooks ● Feb. 14, 2019

And I didn’t know that the enthalpy decrease in a converging passage could be transformed into jet kinetic energy if a divergent passage was added.

From "October Sky" by Homer Hickam

One method involves the use of standard enthalpies and entropies to compute standard free energy changes, ΔG°, according to the following relation.

From Textbooks ● Feb. 14, 2019

Hess’s law can also be used to show the relationship between the enthalpies of the individual steps and the enthalpy of formation.

From Textbooks ● Feb. 14, 2019

We can use bond energies to calculate approximate enthalpy changes for reactions where enthalpies of formation are not available.

From Textbooks ● Feb. 14, 2019

Explain why the enthalpies of vaporization of the following substances increase in the order CH4 < NH3 < H2O, even though all three substances have approximately the same molar mass.

From Textbooks ● Feb. 14, 2019

If we have values for the appropriate standard enthalpies of formation, we can determine the enthalpy change for any reaction, which we will practice in the next section on Hess’s law.

From Textbooks ● Feb. 14, 2019