noun

enthalpy

EN-thal-pee

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Enthalpy (noun) means a measure of the total heat content of a system in thermodynamics, equal to its internal energy plus the product of its pressure and volume; changes in it show how much heat a process gives out or takes in at constant pressure. Example: “The reaction has a negative enthalpy change, so it releases heat.”

noun

technical A measure of the total heat content of a system in thermodynamics, equal to its internal energy plus the product of its pressure and volume; changes in it show how much heat a process gives out or takes in at constant pressure.

"The reaction has a negative enthalpy change, so it releases heat."

"Steam tables list the enthalpy of water at each temperature and pressure."

How to use enthalpy

Learner’s notes

In plain EnglishHow much heat energy something holds.

When to use it

Technical; belongs to chemistry, physics and engineering.

Memory tip

Enthalpy is written H and its change delta H; the plural enthalpies is used for lists of tabulated values.

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Easily confused with

enthalpy vs entropy enthalpy vs internal energy

Common pairings

enthalpy change standard enthalpy of formation enthalpy of vaporisation negative enthalpy

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C2 · Advanced serendipity Fortunate discoveries made entirely by accident.

Gen Z slang rizz Charm — the ability to attract a romantic interest.

B2 · Intermediate empathy The capacity to share another person’s feelings.

C1 · Advanced nonchalant Casually calm and relaxed; unconcerned.

Internet slang delulu Delusional — believing something against the odds.

Etymology nostalgia Greek nostos “return home” + algos “pain”.

C2 · Advanced serendipity Fortunate discoveries made entirely by accident.

Gen Z slang rizz Charm — the ability to attract a romantic interest.

B2 · Intermediate empathy The capacity to share another person’s feelings.

C1 · Advanced nonchalant Casually calm and relaxed; unconcerned.

Internet slang delulu Delusional — believing something against the odds.

Etymology nostalgia Greek nostos “return home” + algos “pain”.

Test yourself on “enthalpy” A quick quiz — meaning, synonyms & usage →

Fill the gap

Can you complete this real example?

The reaction has a negative _____ change, so it releases heat.

Etymology

From Greek enthalpein "to warm in", from en- "in" and thalpein "to heat".

Origin: Greek

Synonyms

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heat content H

Related words

henry hydrogen

Frequently asked questions

What is the difference between enthalpy and entropy?

Enthalpy measures heat content and tells you whether a process absorbs or releases energy. Entropy measures how spread out or disordered that energy is, and together with temperature it decides whether a reaction will actually happen.

What does a negative enthalpy change mean?

It means the system has released heat to its surroundings, so the reaction is exothermic and the products hold less energy than the reactants. A positive change means heat was absorbed and the reaction is endothermic.

Why is only the change in enthalpy measured?

Absolute enthalpy cannot be measured directly, but the difference between the start and end of a process can be, usually as heat exchanged at constant pressure. That is why textbooks always speak of delta H rather than H.

What is the meaning of enthalpy?

"enthalpy" (noun) means a measure of the total heat content of a system in thermodynamics, equal to its internal energy plus the product of its pressure and volume; changes in it show how much heat a process gives out or takes in at constant pressure.

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