Name: internal energy, heat, and work
Uploaded: 2020-09-03T13:38:27.000Z
Duration: 2 min
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Energy

PS.Chm.7.2

Internal Energy

化学プロセスにおいて 反応物と生成物の 内部エネルギーの差は ΔUで表されます 系が反応中に エネルギーを得たか失ったかを 判断するために使用されます ΔUがゼロよりも大きい場合 最終的な内部エネルギーは 初期の内部エネルギーより高く 系は反応中に エネルギーを得たことになります ΔＵがゼロよりも小さい場合 最終的な内部エネルギーは 初期の内部エネルギー よりも低く 系が エネルギーを 失ったことを意味します 熱力学の第一法則によれば 系のエネルギーの変化は その周囲の変化と 反対の変化とのバランスが とれていなければなりません したがって システムの 内部エネルギーの変化は q」で象徴される熱として 伝達されたエネルギーと w」で象徴される仕事として 伝達されたエネルギーとが プロセスの結果 等しくなります 化学では 熱と仕事の 記号は システムが エネルギーを得るか 失うかによって異なります 二酸化炭素の炭素と酸素への 変換を考えてみましょう 反応物は生成物よりも 内部エネルギーが低く ΔUが正であることを意味します エネルギーは周囲から 系に移動し 系の内部エネルギーを 増加させます あるいは 硫黄と酸素ガスを 反応させて 二酸化硫黄を作る際には エネルギーが周囲に移動します ここでは 生成物は反応物よりも 内部エネルギーが低く ΔUは負です したがってΔUは系の初期および 最終的な内部エネルギー状態と 周囲と交換される 熱と仕事の 大きさにのみ依存します

内部エネルギー

物質に存在する可能性のある全種類のエネルギーの合計は、内部エネルギー（ U ）と呼ばれます。これは時に E として表されます。初期内部エネルギーを持つシステムである Uinitial がエネルギーの変化（仕事または熱の移動）を受け、システムの最終内部エネルギーが Ufinalであるとします。 内部エネルギーの変化は、 Ufinal と Uinitialの差と等しくなります。  
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/793/793_Equations-01.png" style="height: 40px;" />
 
 Ufinal とUinitial の値はシステムでは決定できませんが、熱力学の最初の法則は Δ U の値のみを必要とします。 Δ U は Ufinal と Uinitial の値を知らなくても決定できます。 Δ U の正の値は、 Ufinal > Uinitialのときに計算され、システムが周囲からエネルギーを得たことを示します。 Δ U の負の値は、 Ufinal < Uinitial のときに得られ、システムが周囲へとエネルギーを失ったことを示します。 
 
 熱（熱エネルギー）と仕事（機械的エネルギー）は、システムが周囲とエネルギーを交換できる 2 つの異なる方法です。 エネルギーは、周囲から熱（ q ）を吸収するとき、またはシステム上で周囲が仕事（ w ）をするときにシステムに伝達されます。  
 
 たとえば、常温の金属線を熱水に浸したり（線が熱水から熱を吸収する）、線を前後に急速に曲げたりする（線に仕事が加わるため、線が温かくなる）と、線にエネルギーが伝達されます。 いずれも線材の内部エネルギーが増大し、それが線材の温度上昇に反映されます。 逆に、システムから熱が失われた場合、またはシステムが周囲に動きかけた場合、エネルギーはシステムの外に移動します。 例えば、ロケット燃料を燃やすと大量の熱が放出され、また、遠くから力を加えることで周囲に仕事をする（これによりスペースシャトルが地上から離陸する）。 どちらのプロセスでも、システムの内部エネルギーが減少します。 
 
 内部エネルギー、熱、および仕事の関係は、次の式で表されます。 
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/793/793_Equations-02.png" style="height: 40px;" />
 
 これは熱力学の第一法則のひとつで、熱が系に流入・流出したり、仕事が系に行われたりすることで、系の内部エネルギーが変化することを示しています。 熱と仕事の記号は、システムがエネルギーを得るか失うかによって決まります。正のqは周囲から系に流入する熱量であり、負のqは系から流出する熱量です。 仕事 w は、システムに行われた場合は正の値、システムによって行われた場合は負の値となります。 
 
 q と w が両方とも正（ >0 ）の場合、 Δ U は常に正（ >0 ）であり、システムの内部エネルギーが増加します。 q と w の両方が負（ < 0 ）の場合、 Δ Uは常に負（ < 0 ）で、システムの内部エネルギーは減少します。 q と w に異なる符号がある場合、 Δ U の符号は q とwの相対的な大きさに依存します。 
 
 エネルギー、熱、仕事の SI 単位はジュール（ J ）です。 
 
 このテキストは <a href="https://openstax.org/books/chemistry-2e/pages/5-3-enthalpy">、 OpenStax Chemistry 2e 、 Section 5.3: Endarpy から引用</a>しています。

物質に存在するすべての可能な種類のエネルギーの合計は、内部エネルギー(U)と呼ばれ、Eとして象徴されることもあります。

Education

JoVE Core

化学

Thermochemistry

熱化学

KEY TERMS AND CONCEPTS

主要用語と概念

internal energy, heat, and work

Internal energy is the total of all possible kinds of energy in a substance. It is often written as U, and sometimes as E. For a system that changes energy, the important value is the change in internal energy, or ΔU.

ΔU is the difference between the final internal energy and the initial internal energy. The exact values of U final and U initial are usually not known, but the first law of thermodynamics only requires ΔU. A positive ΔU means the system gained energy from the surroundings. A negative ΔU means the system lost energy to the surroundings.

Heat and work are the two ways a system can exchange energy with its surroundings. A system gains energy when it absorbs heat, q, or when the surroundings do work on it, w. For example, a room-temperature metal wire gains energy if it is placed in hot water. It also gains energy if it is bent back and forth quickly, because work is done on it. In both cases, the wire’s internal energy increases, and its temperature rises.

A system loses energy when heat leaves it or when it does work on the surroundings. Burning rocket fuel is one example. It releases a large amount of heat and also does work by pushing on the surroundings over a distance. That is why the system’s internal energy decreases.

The first law of thermodynamics can be written as a relationship between internal energy, heat, and work. It shows that internal energy changes when heat flows into or out of a system or when work is done on or by the system. The sign of q is positive when heat enters the system and negative when heat leaves it. The sign of w is positive when work is done on the system and negative when work is done by the system. When q and w are both positive, ΔU is positive. When q and w are both negative, ΔU is negative. If q and w have different signs, the sign of ΔU depends on which one is larger in magnitude.

The SI unit for energy, heat, and work is the joule, J.

Internal Energy, Heat, and Work

energy basics

How Energy Changes in Chemical Reactions

Chemical reactions change matter and energy at the same time. A match lighting is a simple example. These energy changes are part of everyday life and appear in food, fuels, and industry. Food provides energy through metabolic reactions. The macronutrients in food break down and help keep the body functioning. Fuels such as gasoline, natural gas, and coal are burned to produce energy for transportation, heating, and electricity generation. Industrial chemical reactions also use large amounts...

first law of thermodynamics

Energy Conservation and Internal Energy

Energy conservation describes how energy changes form during chemical and physical changes. Energy can be converted from one form into another, but the energy present before a change still exists in some form after the change is complete. This is the law of conservation of energy. It says energy can neither be created nor destroyed. The law of conservation of matter also applies during chemical change. In most chemical reactions, the total amount of matter does not show a detectable change.

internal energy

Internal energy is the total of all possible kinds of energy in a substance. It is often written as U, and sometimes as E. For a system that changes energy, the important value is the change in internal energy, or ΔU. ΔU is the difference between the final internal energy and the initial internal energy. The exact values of U final and U initial are usually not known, but the first law of thermodynamics only requires ΔU. A positive ΔU means the system gained energy from the surroundings. A...

quantifying heat

Heat Transfer and Specific Heat

Heat transfer and specific heat explain how thermal energy moves and how materials respond to it. Thermal energy is the kinetic energy linked to the random motion of atoms and molecules. Temperature is a measure of how hot or cold a substance is, and it depends on how much thermal energy those particles have. When atoms and molecules move or vibrate faster, their average kinetic energy is higher. That means the object has more thermal energy and a higher temperature. When they move more...

quantifying work

Pressure-Volume Work in Chemistry

Pressure-volume work shows how gas volume changes can transfer energy in chemistry. As a system changes, its internal energy may change too. Energy can move between the system and the surroundings through heat and work. Internal energy, heat, and work are related by an energy equation. Heat depends on a measured temperature change. Work depends on a measured change in volume called pressure-volume work. Work can be defined as a force acting through a distance. Pressure-volume work, also...

enthalpy

Enthalpy and Heat at Constant Pressure

Enthalpy describes heat changes in chemical and physical processes. Chemists use the symbol H for enthalpy. It is defined as a system’s internal energy, E, plus the product of pressure, P, and volume, V. Enthalpy is a state function, so only changes in enthalpy can be measured, not the enthalpy of a substance by itself. For many reactions, the pressure stays constant. Under those conditions, the enthalpy change, ΔH, can be written in a way that includes pressure-volume work. The term PΔV...

thermochemical equations

Heat Changes in Chemical Equations

Heat changes in chemical equations show how much energy a reaction releases or absorbs. At constant pressure, the enthalpy of reaction, or ΔHrxn, is equal to the heat exchanged with the surroundings, qp. Because this value depends on how much reactant takes part, it is an extensive property. The size and sign of ΔHrxn also depend on the reaction itself and on the physical states of the substances involved. An exothermic reaction has a negative ΔHrxn value, while an endothermic reaction has a...

constant pressure calorimetry

Coffee Cup Calorimeter Heat Changes

Coffee cup calorimetry measures heat changes in reactions and physical changes using an insulated calorimeter. The calorimeter is calibrated and designed to limit heat exchange with the outside environment. That makes it possible to measure the heat taken in or released by a substance more accurately, including the energy content of foods. In calorimetry, the system is the substance or substances undergoing change. The surroundings are everything else inside the calorimeter, including the...

constant volume calorimetry

Bomb Calorimeter Heat Measurement

Bomb calorimetry measures the heat released by reactions that produce a lot of energy, especially combustion reactions. A coffee cup calorimeter works at constant pressure and is useful for reactions in solution. A bomb calorimeter works at constant volume and is used for reactions that make large amounts of heat and gaseous products. The word "bomb" refers to the strong, explosive force some reactions can have. In a bomb calorimeter, the volume does not change, so 94V = 0. That means the...

hess's law

Calculating Reaction Heat with Hess's Law

Calculating reaction heat with Hess's law lets chemists find enthalpy changes without measuring every reaction directly. Some reactions are hard or impossible to test in the lab. Even when a reaction can be measured, it is often easier to calculate the heat change from other known enthalpy values. Hess's law says that if a process can be written as the sum of several stepwise processes, the enthalpy change for the total process equals the sum of the enthalpy changes for the steps. This works...

standard enthalpy of formation

Using Standard Enthalpy Values in Chemistry

Enthalpy changes are often listed for reactions that start and end under the same conditions. Chemists use a standard state as a reference set of conditions for comparing properties. In IUPAC terms, the standard state means 1 bar of pressure and 1 M solutions, but it does not set a temperature. Many thermochemical tables still use 1 atm as the reference pressure. Because the difference between 1 bar and 1 atm is very small, enthalpy change usually stays almost the same. A superscripted o in...

enthalpies of reaction

Calculating reaction heat with Hess's law uses standard enthalpies of formation to find the enthalpy change of a reaction. When the formation values for the reactants and products are known, the overall reaction can be broken into simpler stepwise reactions. This approach helps show how the heat change for the full reaction is built from smaller parts. First, the reactants are thought of as being decomposed into their component elements. The enthalpy change for this step is proportional to the...

key terms and concepts

Explore how internal energy changes through heat and work, plus the sign rules for q, w, and ΔU in the first law of thermodynamics.

Internal Energy, Heat, and Work | JoVE K12

chemistry

JoVE Core 化学は、簡潔で理解しやすいアニメーションビデオレッスンを使用して、一般的な化学の概念を生き生きとしたものにします。さらに、活動する科学者のビデオでは、現在世界中の実験室で行われている古典的そして独創的な研究・実験をお見せします。

Matter and its Interactions

PS.Chm.4.1

Louisiana Student Standards for Science

High School

HS-PS3-1

HS-PS3-3

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Virginia  Standards of Learning

HIgh School

CH.7

CH.7.a

Texas Essential Knowledge and Skills

CHEM.13

CHEM.13.A

CHEM.13.C

Next Generation Science Standards

Physical Science

Florida Department of Education

SC.912.P.10

SC.912.P.10.1

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

Physics

P-PS3-1

P-PS3-2

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Energy

HS-PS3-1.

Classifying Matter by State

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Classifying Matter by Composition

Matter: Pure Substances and Mixtures
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physical-and-chemical-properties-of-matter

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Physical Properties of Matter

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Intermolecular vs Intramolecular Forces

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Intermolecular Forces

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Surface Tension, Capillary Action, and Viscosity

Surface Tension
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States of Matter and Phase Changes

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Phase Transitions

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Phase Transitions: Vaporization and Condensation

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Vapor Pressure

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Clausius-Clapeyron Equation

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Phase Transitions: Melting and Freezing

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phase-transitions-sublimation-and-deposition

Phase Transitions: Sublimation and Deposition

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Heating and Cooling Curves

When a substance&#8212;isolated from its environment&#8212;is subjected to heat changes, corresponding changes in temperature and phase of the substance ...

Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. ...

Use models to explain how changes in energy affect the arrangement and movement of the particles in solids, liquids, and gases, as well as the relative strengths of their intermolecular forces.

PS.Chm.7.1

Energy Basics

Chemical reactions, such as those that occur when you light a match, involve changes in energy as well as matter.

Chemical changes and their accompanying ...

First Law of Thermodynamics

Energy Conservation

Energy can be converted from one form into another, but all of the energy present before a change occurs always exists in some form ...

The total of all possible kinds of energy present in a substance is called the internal energy (U), sometimes symbolized as E. Suppose a system with ...

Quantifying Heat

Thermal Energy&#160;

Microscopically, thermal energy is the kinetic energy associated with the random motion of atoms and molecules. Temperature is a ...

Quantifying Work

As a system undergoes a change, its internal energy can change, and energy can be transferred from the system to the surroundings, or from the ...

Enthalpy

Chemists ordinarily use a property known as enthalpy (H) to describe the thermodynamics of chemical and physical processes. Enthalpy is defined as the sum ...

Thermochemical Equations

For a chemical reaction (the system) carried out at constant pressure &ndash; with the only work done caused by expansion or contraction &ndash; the ...

Constant Pressure Calorimetry

Calorimetry is a technique used to measure the amount of heat involved in a chemical or physical process or to measure the heat transferred to or from a ...

Constant Volume Calorimetry

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using-differential-scanning-calorimetry-to-measure-changes-in-enthalpy

Using Differential Scanning Calorimetry to Measure Changes in Enthalpy

Source: Laboratory of Dr. Terry Tritt &#8212; Clemson University
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Hess's Law

There are two ways to determine the amount of heat involved in a chemical change: measure it experimentally, or calculate it from other experimentally ...

Standard Enthalpy of Formation

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Enthalpies of Reaction

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Chemical Stoichiometry and Gases: Using Ideal Gas Law to Determine Moles

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Basic Postulates of Kinetic Molecular Theory: Particle Size, Energy, and Collision

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Kinetic Molecular Theory and Gas Laws Explain Properties of Gas Molecules

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Kinetic Molecular Theory: Molecular Velocities, Temperature, and Kinetic Energy

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Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion

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Real Gases: Effects of Intermolecular Forces and Molecular Volume Deriving Van der Waals Equation

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Ideal Gas Law

Source: Laboratory of Dr. Andreas Z&#252;ttel - Swiss Federal Laboratories for Materials Science and Technology
The ideal gas law describes the behavior ...

Derivation of the Ideal Gas Law
Gases are a fundamental state of matter. A gas is a collection of molecules that have a significant distance between their ...

Source: Smaa Koraym at Johns Hopkins University, MD, USA

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Source: Smaa Koraym at Johns Hopkins University, MD, USA

	Determining the Mass of the Unknown LiquidExpand
	According to the ideal gas law for a given ...

Use mathematics and computational thinking to explain the relationships among pressure, temperature, volume, and quantity of gas, both qualitatively and quantitatively.

PS.Chm.7.3

Understand the relationship among pressure, temperature, volume, and phase.

Internal Energy, Heat, and Work

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