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

Im Wesentlichen gibt es drei verschiedene Phasen der Materie: fest, flüssig und gasförmig.
Beim Ändern der Temperatur geht ein Zustand in einen anderen über. Dieses Phänomen wird als Phasenwechsel bezeichnet, der in der Natur reversibel ist.
Beim Erhitzen verwandelt sich ein Feststoff in eine Flüssigkeit, dieser Vorgang wird als Schmelzen bezeichnet, während umgekehrt als Gefrieren bezeichnet wird.
Die Wärme, die in diesem Übergang für ein Material der Masse 'm' absorbiert oder freigesetzt wird, kann unter Verwendung der Schmelzwärme bewertet werden, die die Energie pro Masseneinheit ist, die beim Phasenwechsel benötigt oder freigesetzt wird.
Wenn eine Flüssigkeit erhitzt wird, wandelt sie sich in ein Gas um, und der Vorgang wird als Verdampfen oder Sieden bezeichnet. Beim Abkühlen wird die Umwandlung eines Gases in eine Flüssigkeit als Kondensation bezeichnet.
Die Energie pro Masseneinheit, die beim Phasenwechsel zwischen Flüssigkeit und Gas benötigt oder freigesetzt wird, wird als Verdampfungswärme bezeichnet, wobei Q die aufgenommene oder freigesetzte Wärme ist.
Einige der Materialien wie Trockeneis können direkt einen Übergang von fest zu gasförmig haben, was als Sublimation bezeichnet wird.

<ol>
	<li>OpenStax. (2019). Universitätsphysik Vol. 2. [Webversion]. Abgerufen von <a href="https://openstax.org/details/books/university-physics-volume-2">https://openstax.org/details/books/university-physics-volume-2</a>; S. 28–31.</li>
</ol>

phasenänderungen

Phasenübergänge spielen eine wichtige theoretische und praktische Rolle bei der Untersuchung von Wärmefluss. Beim Schmelzen oder fusionieren wird ein Feststoff zu einer Flüssigkeit; der umgekehrte Prozess ist das Gefrieren. Beim Verdampfen wird eine Flüssigkeit zu einem Gas; der umgekehrte Prozess ist die Kondensation.

Eine Substanz schmilzt oder gefriert bei einer Temperatur, die als Schmelzpunkt bezeichnet wird, und siedet oder kondensiert bei ihrem Siedepunkt. Diese Temperaturen hängen vom Druck ab. Hoher Druck begünstigt die dichtere Form der Substanz, daher erhöht hoher Druck typischerweise den Schmelzpunkt und den Siedepunkt, während niedriger Druck sie senkt.

Beispielsweise beträgt der Siedepunkt von Wasser bei 1,00 atm 100 °C. Bei höherem Druck ist der Siedepunkt höher und bei niedrigerem Druck ist er niedriger. Die Hauptausnahme bildet das Schmelzen und Gefrieren von Wasser.

Die Energie, die bei einer Phasenänderung beteiligt ist, hängt von der Anzahl der Bindungen oder Kraftpaaren und deren Stärke ab. Die Anzahl der Bindungen ist proportional zur Anzahl der Moleküle und somit zur Masse der Probe. Die pro Masseneinheit erforderliche Energie, um eine Substanz von der festen Phase in die flüssige Phase zu ändern oder die freigesetzt wird, wenn die Substanz von flüssig zu fest wechselt, wird als Schmelzwärme bezeichnet. Die pro Masseneinheit erforderliche Energie, um eine Substanz von der flüssigen Phase in die gasförmige Phase zu ändern, wird als Verdampfungswärme bezeichnet. Weiterhin sind die latente Schmelzwärme und die latente Verdampfungswärme Stoffkonstanten, die experimentell bestimmt werden können. Diese Konstanten sind "latent", oder verborgen, da in Phasenänderungen Energie ein- oder austritt, ohne eine Änderung der Temperatur im System zu verursachen; die Energie ist also effektiv verborgen.

Phasenänderungen

Phasenübergänge spielen eine wichtige theoretische und praktische Rolle bei der Untersuchung des Wärmeflusses. Beim Schmelzen oder Schmelzen verwandelt sich ein Feststoff in eine Flüssigkeit; das...

Education

Lehre

JoVE Core

Physik

Unit 1

Einheit 1

Temperature and Heat

Temperatur und Wärme

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

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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Thermal expansion and thermal stress are shown through the Golden Gate Bridge. The bridge faces temperatures from -15 °C to 40 °C. At its coldest, the main span is 1275 m long. Assuming the bridge is made entirely of steel, the example asks for the change in its length across this temperature range. To solve the problem, the known values must be identified first. The initial length is 1275 m. The coefficient of linear expansion for steel is 12 x 10 -6 /°C, and the change in temperature is 55...

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Heat is energy transferred because of a temperature difference, and it can change an object’s temperature. Since heat is energy, its SI unit is the joule (J). Heat transfer is the movement of energy from one place or material to another, and it plays a role in home heating, cooking, and many industrial processes. Two common units for heat are the calorie and the kilocalorie. A calorie (cal) is the energy needed to change the temperature of 1 g of water by 1 °C, specifically between 14.5 °C and...

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

Heat Exchange in an Insulated System

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

Convection and Radiation in Heat Transfer

Convection and radiation are two major ways heat moves. In convection, thermal energy is carried by the large-scale flow of matter. Warm air and water rise because they are less dense, so ocean currents and large-scale atmospheric circulation move heat from the tropics toward the poles and move cold air from the poles toward the tropics. Earth’s rotation changes these moving air currents. It interacts with the flow and helps produce the eastward movement of air in the temperate zones.

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 Physics introduces the theory and application of fundamental physics topics, including kinematics, dynamics, fluid mechanics, statics, waves, and acoustics, with concise and easy-to-understand animated videos. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

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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