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

Прежде всего, существуют три различные фазы вещества: твердое, жидкое и газообразное.
При изменении температуры одно состояние переходит в другое. Это явление называется фазовым переходом, который является обратимым по своей природе.
При нагревании твердое вещество переходит в жидкость, этот процесс называется плавлением, в то время как наоборот называется замораживанием.
Тепло, поглощенное или высвобожденное при этом переходе для материала с массой 'm', может быть оценено с помощью теплоты плавления, которая представляет собой энергию на единицу массы, требуемую или высвобождаемую при фазовом переходе.
Точно так же, если жидкость нагревается, она превращается в газ, и этот процесс называется испарением или кипячением. При охлаждении превращение газа в жидкость называется конденсацией.
Энергия на единицу массы, необходимая или высвобождаемая при фазовом переходе между жидкостью и газом, называется теплотой испарения, где Q — это тепло, поглощенное или высвобожденное.
Некоторые материалы, такие как сухой лед, могут напрямую переходить из твердого состояния в газообразное, что называется сублимацией.

<ol>
	<li>OpenStax. (2019). Университетская физика Том 2. [Веб-версия]. Получено из <a href="https://openstax.org/details/books/university-physics-volume-2">https://openstax.org/details/books/university-physics-volume-2</a>; С. 28–31.</li>
</ol>

Фазовые переходы

Фазовые переходы играют важную теоретическую и практическую роль в изучении теплового потока. При плавлении или слиянии, твёрдое вещество превращается в жидкое; обратный процесс - замерзание. При испарении жидкость превращается в газ; обратный процесс - конденсация.

Вещество плавится или замерзает при определённой температуре, называемой точкой плавления, и кипит или конденсируется при точке кипения. Эти температуры зависят от давления. Повышенное давление способствует более плотной форме вещества, поэтому обычно повышенное давление повышает точку плавления и точку кипения, а пониженное давление их снижает.

Например, точка кипения воды составляет 100 °C при 1,00 атм. При более высоком давлении точка кипения выше, а при более низком давлении она ниже. Основное исключение составляет плавление и замерзание воды.

Энергия, связанная с фазовым переходом, зависит от количества связей или пар сил и их прочности. Количество связей пропорционально числу молекул и, следовательно, массе образца. Энергия, расходуемая на единицу массы для превращения вещества из твёрдой фазы в жидкую фазу или высвобождаемая при изменении вещества из жидкой в твёрдую фазу, называется теплотой плавления. Энергия, расходуемая на единицу массы для превращения вещества из жидкой фазы в паровую фазу, называется теплом испарения. Кроме того, скрытая энергия плавления и скрытая энергия испарения являются материальными постоянными, которые могут быть определены экспериментально. Эти постоянные являются "скрытыми", потому что в фазовых переходах энергия входит или покидает систему, не вызывая изменения температуры в системе; таким образом, энергия находится в скрытом состоянии.

Фазовые переходы играют важную теоретическую и практическую роль в изучении теплового потока. При плавлении или плавлении твердое вещество превращается в жидкость; тем...

Education

JoVE Core

Физика

Unit 1

Раздел 1

Temperature and Heat

Температура и тепло

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

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 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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Mechanisms of Heat Transfer II

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1 Exploring phenomena or engineering problems
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Heat and Phase Change Energy

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