# Latent heat

## Information about Latent heat

In thermochemistry, latent heat is the amount of energy in the form of heat released or absorbed by a substance during a change of phase (i.e. solid, liquid, or gas), - also called a phase transition.<ref name="Perrot" >Perrot, Pierre (1998). A to Z of Thermodynamics. Oxford University Press. ISBN 0-19-856552-6. [1]

The term was introduced around 1750 by Joseph Black as derived from the Latin latere, to lie hidden. The term is now obsolete, replaced by "enthalpy of transformation".

Two latent heats (or enthalpies) are typically described: latent heat of fusion (melting), and latent heat of vaporization (boiling). The names describe the direction of heat flow from one phase to the next: solid → liquid → gas.

The change is endothermic, i.e. the system absorbs energy, when the change is from solid to liquid to gas. It is exothermic (the process releases energy) when it is in the opposite direction. For example, in the atmosphere, when a molecule of water evaporates from the surface of any body of water, energy is transported by the water molecule into a lower temperature air parcel that contains more water vapor than its surroundings. Because energy is needed to overcome the molecular forces of attraction between water particles, the process of transition from a parcel of water to a parcel of vapor requires the input of energy causing a drop in temperature in its surroundings. If the water vapor condenses back to a liquid or solid phase onto a surface, the latent energy absorbed during evaporation is released as sensible heat onto the surface. The large value of the enthalpy of condensation of water vapor is the reason that steam is a far more effective heating medium than boiling water, and is more hazardous.

## Latent Heat Equation

The equation for latent heat is:

Q = mL

where:

Q is the amount of energy required to change the phase of the substance,
m is the mass of the substance,
L is the specific latent heat for a particular substance.

In other words, specific latent heat is found when energy is divided by mass.

## Table of latent heats

Latent heats and change of phase temps of common fluids and gases
Substance Latent Heat
Fusion
J/g
Melting
Temp
°C
Latent Heat
Vaporization
J/g
Boiling
Temp
°C
Alcohol, Ethyl108-11485578.3
Ammonia339-751369-33.34
Carbon Dioxide184-57574-78
Helium21-268.93
Hydrogen58-259455-253
Nitrogen25.7-210200-196
Oxygen13.9-219213-183
Toluene-93351110.6
Turpentine293
Water33402272100

## References

1. ^ Clark, John, O.E. (2004). The Essential Dictionary of Science. Barnes & Noble Books. ISBN 0-7607-4616-8.

In thermodynamics and physical chemistry, thermochemistry is the study of the heat evolved or absorbed in chemical reactions. Thermochemistry, generally, is concerned with the heat exchange accompanying transformations, such as mixing, phase transitions, chemical reactions, etc.
energy (from the Greek ενεργός, energos, "active, working")[1] is a scalar physical quantity that is a property of objects and systems of objects which is conserved by nature.
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In the physical sciences, a state of matter is one of the many ways that matter can interact with itself to form a macroscopic, homogenous phase. The most familiar examples of states of matter are solids, liquids, gases, and plasmas; the most common state of matter in the visible
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Joseph Black (April 16,1728 - December 6,1799) was a Scottish physicist and chemist, known for his discoveries of latent heat, specific heat, and carbon dioxide. He was a founder of thermochemistry who developed many pre-thermodynamics concepts, such as heat capacity, and was the
In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or ΔH, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the "useful" work
The enthalpy of fusion (symbol: ), also known as the heat of fusion or specific melting heat, is the amount of thermal energy which must be absorbed or evolved for 1 mole of a substance to change states from a solid to a liquid or vice versa.
Melting is a process that results in the phase change of a substance from a solid to a liquid. The internal energy of a solid substance is increased (typically by the application of heat) to a specific temperature (called the melting point) at which it changes to the liquid phase.
The enthalpy of vaporization, (symbol ), also known as the heat of vaporization or heat of evaporation, is the energy required to transform a given quantity of a substance into a gas.
Boiling, a type of phase transition, is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental
endothermic describes a process or reaction that absorbs energy in the form of heat. Its etymology stems from the Greek prefix endo-, meaning “inside” and the Greek suffix –thermic, meaning “to heat”.
In thermodynamics, the word exothermic describes a process or reaction that releases energy in the form of heat. Its etymology stems from the Greek prefix ex-, meaning “outside” and the Greek word thermein, meaning “to heat”.
Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity. It contains roughly (by molar content/volume) 78% nitrogen, 20.95% oxygen, 0.93% argon, 0.
Water is a common chemical substance that is essential to all known forms of life.[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor.

### Definition

An air parcel is an imaginary volume of air used by meteorologists to conceptualize the thermodynamic fluid motions of the atmosphere for use in weather forecasting.
Water vapor or water vapour (see spelling differences), also aqueous vapor, is the gas phase of water. Water vapor is one state of the water cycle within the hydrosphere.
In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i.e. density, crystal structure, index of refraction, and so forth).
Sensible heat is potential energy in the form of thermal energy or heat. The thermal body must have a temperature higher than its surroundings, (also see: latent heat). The thermal energy can be transported via conduction, convection, radiation or by a combination thereof.
Ethanol, also known as ethyl alcohol, drinking alcohol or grain alcohol, is a flammable, colorless, slightly toxic chemical compound, and is best known as the alcohol found in alcoholic beverages.
Ammonia is a compound with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of the planet as a precursor to foodstuffs and fertilizers.
Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state.
Helium (He) is a colorless, odorless, tasteless, non-toxic, inert monatomic chemical element that heads the noble gas series in the periodic table and whose atomic number is 2.
1, −1
(amphoteric oxide)
Electronegativity 2.20 (Pauling scale) More

Atomic radius 25 pm
Atomic radius (calc.) 53 pm
Covalent radius 37 pm
Van der Waals radius 120 pm
Miscellaneous

Thermal conductivity (300 K) 180.
3, 5, 4, 2
(strongly acidic oxide)
Electronegativity 3.04 (Pauling scale)
Ionization energies
(more) 1st: 1402.3 kJmol−1
2nd: 2856 kJmol−1
3rd: 4578.1 kJmol−1

Atomic radius 65 pm
2, −1
(neutral oxide)
Electronegativity 3.44 (Pauling scale)
Ionization energies
(more) 1st: 1313.9 kJmol−1
2nd: 3388.3 kJmol−1
3rd: 5300.5 kJmol−1

Atomic radius 60 pm