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

主に、物質には固体、液体、気体の3つの異なる相があります。
温度を変更すると、1つの状態が別の状態に変わります。この現象は相変化と呼ばれ、本質的に可逆的です。
加熱すると、固体が液体に変化するこのプロセスは溶融と呼ばれ、その逆は凍結と呼ばれます。
質量「m」の材料について、この遷移で吸収または放出される熱は、相変化で必要または放出される単位質量あたりのエネルギーである融解熱を使用して評価できます。
同様に、液体が加熱されると、それは気体に変換され、このプロセスは気化または沸騰と呼ばれます。冷却時には、気体が液体に変化することを凝縮と呼びます。
液体と気体の間の相変化で必要または放出される単位質量あたりのエネルギーは、気化熱と呼ばれ、Qは吸収または放出される熱です。
ドライアイスのような一部の材料は、昇華と呼ばれる固体から気体への直接遷移を起こすことがあります。

<ol>
	<li>OpenStaxです。(2019). 大学物理学 Vol.2.【Web版】。<a href="https://openstax.org/details/books/university-physics-volume-2">https://openstax.org/details/books/university-physics-volume-2 から取得</a>。28〜31ページ。</li>
</ol>

相変化

相転移は、熱流の研究において理論的および実践的に重要な役割を果たします。 融解または融合では、固体は液体に変わります。 逆のプロセスはフリーズします。 蒸発では、液体は気体に変わります。 反対のプロセスは凝縮です。

物質は、融点と呼ばれる温度で溶けたり凍ったり、沸点で沸騰したり凝縮したりします。 これらの温度は圧力に依存します。 高圧では物質の密度が高まるため、通常、高圧では融点と沸点が上昇し、低圧では融点と沸点が低下します。

たとえば、水の沸点は 1.00 気圧で 100℃です。 圧力が高くなると沸点は高くなり、圧力が低くなると沸点は低くなります。 主な例外は、水の融解と凍結です。

相変化に関係するエネルギーは、結合または力のペアの数とその強さに依存します。 結合の数は分子の数に比例し、したがってサンプルの質量に比例します。 物質を固相から液相に変化させるのに必要な単位質量当たりのエネルギー、または物質が液体から固体に変化するときに放出されるエネルギーは、融解熱として知られています。 物質を液相から気相に変化させるのに必要な単位質量当たりのエネルギーは蒸発熱として知られています。 さらに、融解潜熱と蒸発潜熱は実験的に決定できる材料定数です。 これらの定数は「潜在的」、つまり隠蔽されています。これは、相変化では、系に温度変化を引き起こすことなくエネルギーが系に出入りするためです。 したがって、事実上、エネルギーは隠蔽されます。

相転移は、熱流の研究において理論的および実用的な重要な役割を果たします。融解または融合では、固体は液体に変わります。ザ。。。

Education

JoVE Core

物理学

Unit 1

ユニット1

Temperature and Heat

温度と熱

KEY TERMS AND CONCEPTS

主要用語と概念

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

temperature and thermal equilibrium

Heat, Temperature, and Everyday Energy

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...

zeroth law of thermodynamics

Thermal Equilibrium and the Zeroth Law

The zeroth law of thermodynamics explains thermal equilibrium between objects. If object A is in equilibrium with object B, and object B is in equilibrium with object C, then object A is also in equilibrium with object C. This transitive relationship is the key idea behind the law. A simple example uses metal blocks and a metal plate at room temperature. A cold metal block and a hot metal block are both placed on the plate. Over time, the cold block and the plate reach thermal equilibrium, and...

thermometers and temperature scales

How Thermometers Measure Heat

Thermometers measure temperature by using physical properties that change in a predictable way. One common example is volume. For most substances, volume increases as temperature rises. That idea is used in alcohol thermometers and in the original mercury thermometers. Other thermometer designs use different temperature-sensitive properties. Some measure electrical resistance, color, or the emission of infrared radiation. The alcohol thermometer is a common example. It contains red-dyed...

gas thermometers and the kelvin scale

Kelvin Temperature and Gas Thermometer Standards

Kelvin temperature is the absolute scale used in science, and it starts at absolute zero. That zero point matches the lowest possible temperature, where molecular motion reaches zero or the minimum allowed by quantum mechanics. Scientists use this scale because some physical quantities, such as the volume of an ideal gas, depend directly on absolute temperature. The Kelvin scale is part of the SI system of units, so its definition is more precise than simply using water’s freezing and boiling...

thermal expansion

Thermal Expansion in Air, Water, and Solids

Thermal expansion is the change in size or volume of a material as its temperature changes. A common example is the alcohol inside a thermometer. As the temperature rises, the alcohol expands and shows the change. Heated air also expands. It becomes less dense than the cooler air around it, so the surrounding air pushes it upward. This is why steam and smoke rise and why hot air balloons float. The same effect happens in liquids and gases, and it helps move heat upward in homes, oceans, and...

thermal stress

How Temperature Changes Create Stress

Thermal stress is the stress that builds up when an object changes temperature but cannot expand or contract freely. If the object would expand without restraint, the stress is compressive. If it would contract, the stress is tensile. This stress from heating or cooling can become large enough to cause damage. Engineers often reduce it by designing parts so they can move as temperature changes. Highway blocks, for example, are separated by gaps so thermal stress does not build up. When gaps...

thermal expansion and thermal stress: problem solving

thermal-expansion-and-thermal-stress-problem-solving

Golden Gate Bridge Thermal Expansion

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...

heat flow and specific heat

Heat Units and Specific Heat

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

Three Ways Heat Moves Between Objects

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

Heat Transfer Calculations with Conduction, Convection

Heat transfer calculations with conduction and convection use the temperature difference to find the rate of heat flow. Radiation can also be part of the process. The main idea is that heat moves only because one area is hotter than another, and a larger temperature difference leads to faster transfer. To solve a heat transfer problem, first identify the type of transfer involved. It may be conduction, convection, radiation, or a combination of all three. Next, write down the unknown...

radiation: applications

Earth’s Energy Balance and Greenhouse Effect

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 物理学は、運動学、力学、流体力学、静力学、波動、音響などの基礎的な物理学の理論と応用を、簡潔でわかりやすいアニメーション ビデオで紹介します。さらに、科学者の実際のビデオでは、世界中の今日の研究所で行われている古典的および独自の研究実験における関連概念の適用を示しています。

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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