Name: heat and phase change energy
Uploaded: 2023-04-30T12:29:47.000Z
Duration: 1 min 19 s
Channel: JoVE

K12 Standards

Minnesota Academic Standards in Science

9-12

Physics

1.2.1 9C.4.2.1.2

Phase Changes

Il existe principalement trois phases différentes de la matière : solide, liquide et gazeuse.
Lors du changement de température, un état se transforme en un autre. Ce phénomène est appelé changement de phase, qui est de nature réversible.
Lors du chauffage, un solide se transforme en liquide, ce processus est appelé fusion, tandis que l’inverse est appelé congélation.
La chaleur absorbée ou libérée dans cette transition pour un matériau de masse « m » peut être évaluée à l'aide de la chaleur de fusion, qui est l'énergie par unité de masse requise ou libérée lors du changement de phase.
De même, si un liquide est chauffé, il se transforme en gaz, et le processus est appelé vaporisation ou ébullition. Lors du refroidissement, la transformation d’un gaz en liquide est appelée condensation.
L’énergie par unité de masse requise ou libérée lors du changement de phase entre le liquide et le gaz est appelée chaleur de vaporisation, où Q est la chaleur absorbée ou libérée.
Certains matériaux comme la glace sèche peuvent avoir directement une transition de l’état solide au gaz, ce qu’on appelle la sublimation.

<ol>
	<li>OpenStax. (2019). Physique universitaire Vol. 2. [Version Web]. Récupéré de <a href="https://openstax.org/details/books/university-physics-volume-2">https://openstax.org/details/books/university-physics-volume-2</a> ; p. 28 à 31.</li>
</ol>

changements de phase

Les transitions de phase jouent un rôle théorique et pratique important dans l'étude du flux de chaleur. Lors de la fusion, un solide se transforme en liquide ; le processus inverse est la solidification. Lors de l'évaporation, un liquide se transforme en gaz ; le processus inverse est la condensation.

Une substance fond ou se solidifie à une température appelée son point de fusion et bout ou se condense à son point d'ébullition. Ces températures dépendent de la pression. Une pression élevée favorise la forme la plus dense de la substance, donc généralement, une pression élevée augmente le point de fusion et le point d'ébullition, et une pression faible les abaisse.

Par exemple, le point d'ébullition de l'eau est de 100°C à 1,00 atm. À des pressions plus élevées, le point d'ébullition est plus élevé, et à des pressions plus basses, il est plus bas. La principale exception concerne la fusion et la solidification de l'eau.

L'énergie impliquée dans un changement de phase dépend du nombre de liaisons ou de paires de forces et de leur force. Le nombre de liaisons est proportionnel au nombre de molécules et, par conséquent, à la masse de l'échantillon. L'énergie par unité de masse requise pour changer une substance de la phase solide à la phase liquide, ou libérée lorsque la substance change de liquide à solide, est appelée chaleur de fusion. L'énergie par unité de masse requise pour changer une substance de la phase liquide à la phase vapeur est appelée chaleur de vaporisation. De plus, la chaleur latente de fusion et la chaleur latente de vaporisation sont des constantes matérielles qui peuvent être déterminées expérimentalement. Ces constantes sont "latentes", ou cachées, car lors des changements de phase, l'énergie entre ou quitte un système sans provoquer de changement de température dans le système ; ainsi, l'énergie est en quelque sorte cachée.

Changements de phase

Les transitions de phase jouent un rôle théorique et pratique important dans l’étude des flux de chaleur. Lors de la fusion ou de la fusion, un solide se transforme en liquide ; le...

Education

Enseignement

JoVE Core

Physique

Unit 1

Unité 1

Temperature and Heat

Température et chaleur

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

heat and phase change energy

Heat and phase change energy explain why substances melt, freeze, boil, and condense. A solid turns into a liquid during melting, also called fusion. The reverse process is freezing. A liquid turns into a gas during evaporation. The reverse process is condensation.

Each substance changes phase at specific temperatures. The melting point is the temperature where a substance melts or freezes. The boiling point is the temperature where a substance boils or condenses. These temperatures depend on pressure. In most cases, higher pressure raises the melting point and boiling point because it favors the denser form of the substance. Lower pressure usually lowers them.

Water shows a useful example. At 1.00 atm, water boils at 100 °C. At higher pressures, its boiling point is higher. At lower pressures, its boiling point is lower. Water is also the main exception to the usual pattern for melting and freezing.

Phase changes also involve energy. The amount of energy depends on the number of bonds, or force pairs, and on their strength. Because the number of bonds depends on the number of molecules, the energy needed also depends on the mass of the sample. The energy per unit mass needed to change a solid into a liquid, or released when a liquid becomes a solid, is called the heat of fusion. The energy per unit mass needed to change a liquid into a vapor is called the heat of vaporization.

The latent heat of fusion and the latent heat of vaporization are material constants. They can be measured experimentally. These heats are called latent, or hidden, because energy enters or leaves the system during a phase change without changing the temperature. In that sense, the energy is hidden.

Heat and Phase Change Energy

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Heat and temperature are key ideas in thermodynamics and in everyday life. People often connect temperature with hot and cold, but science gives it a more precise meaning. Temperature is the quantity measured with a thermometer. It is also linked to the average translational kinetic energy of particles. Heat is different from temperature. Heat is energy that moves from one place or material to another because there is a difference in temperature. That difference in temperature keeps heat...

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phase changes

Heat and phase change energy explain why substances melt, freeze, boil, and condense. A solid turns into a liquid during melting, also called fusion. The reverse process is freezing. A liquid turns into a gas during evaporation. The reverse process is condensation. Each substance changes phase at specific temperatures. The melting point is the temperature where a substance melts or freezes. The boiling point is the temperature where a substance boils or condenses. These temperatures depend on...

calorimetry

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Calorimetry studies heat exchange in an insulated system. A calorimeter is a container that prevents heat transfer in or out. Scientists use calorimetry to measure heat and specific heat capacity. A calorimetry problem is any situation where the objects are thermally isolated from their surroundings. The key idea comes from conservation of energy. During heat transfer, the heat gained by the colder object must equal the heat lost by the hotter object. A simple example is water poured into a...

mechanisms of heat transfer i

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Heat transfer happens when there is a temperature difference. It can move fast, like through a cooking pan, or slowly, like through the walls of a picnic ice box. Heat transfer appears in many everyday situations, so it is hard to find a place where it does not occur. There are only three ways heat is transferred: conduction, convection, and radiation. A fireplace shows all three at once. Radiation carries most of the heat into the room. Conduction also moves heat into the room, but much more...

mechanisms of heat transfer ii

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conduction, convection and radiation: problem solving

conduction-convection-and-radiation-problem-solving

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radiation: applications

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Earth’s energy balance and the greenhouse effect help explain its average temperature. Earth is in radiative contact with both the Sun and dark space. It receives almost all of its energy from solar radiation, and it reflects some of that energy back into outer space. Dark space is very cold, about 3 K, so Earth also radiates energy into it. Heat can move quickly from soil and grasses, and frost can form on clear summer evenings, even in warm latitudes. In a first approximation, Earth’s...

absorption of radiation

Radiation Heat Transfer and Thermographs

Radiation heat transfer depends on temperature, surface area, and emissivity. The Stefan-Boltzmann law describes the rate of heat transfer by emitted radiation. In this law, σ is the Stefan-Boltzmann constant, A is the object’s surface area, and T is its temperature in kelvins. The fourth-power dependence on absolute temperature makes radiation highly sensitive to small temperature changes. Even a slight rise in temperature can change the emitted heat a lot. That sensitivity is why radiation...

key terms and concepts

Explore melting, freezing, boiling, and condensation, plus how pressure changes melting and boiling points and why latent heat stays hidden.

Heat and Phase Change Energy | JoVE K12

physics

JoVE Core Physique présente plusieurs branches de la physique fondamentale grâce à des vidéos animées concises et faciles à comprendre ; cela inclut: la cinématique, la dynamique, la mécanique des fluides, la mécanique statique, les ondes et l'acoustique. En parallèle, les vidéos de scientifiques à l'action démontrent l'application de concepts associés à ces domaines dans des expériences de recherche classiques et originales réalisées dans des laboratoires modernes du monde entier.

Arizona Science Standards

High School

Physical Science

HS+Phy.P4

HS+Phy.P4U1.6

Texas Essential Knowledge and Skills

Chemistry

CHEM.13

CHEM.13.D

Alabama Course of Study Science

Earth and Space Science

Earth's Systems

9-12.ESS.2.7

9-12.ESS.2.7.a

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Heat and Phase Change Energy

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