Name: pressure-volume work in chemistry
Uploaded: 2020-09-03T13:38:27.000Z
Duration: 2 min 30 s
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

Quantifying Work

システムの内部エネルギーは 熱と仕事の合計として 定義されていることを 思い出してください 熱は熱量計を使って 測定されますが 仕事はどのように 定量化されるのでしょうか？仕事は物体が受ける力の結果で 例えば 押されたり引かれたり 持ち上げられたりすることで 移動することです したがって 仕事は 力と距離に積に等しくなります 仕事の例はボールを ゴルフクラブで動かすことです エネルギーはクラブから ボールに移ります この場合 ボールは 周囲によって仕事が 実行される系です 化学反応では 仕事は系内の 複数の物理的または 化学的変化に 関連させることができます よくある仕事のタイプは 圧力-体積の仕事です エンジンのシリンダー内での 燃焼を考えてみましょう 燃焼は熱を 発生させるだけでなく ガスを発生させ これが仕事を行います シリンダー内のガスの 体積が膨張すると 周囲の外力に抗して ガスの圧力が ピストンを下に押し下げます 圧力とは ある面積に 作用する力と定義されています ここでは 膨張する 気体からの力は ピストンの底面の面に 分布しています つまり 力は 圧力×面積」です したがって 力×距離」である仕事は 圧力に作用する面積 と距離を乗じたものとして 書き換えることができます エンジンのシリンダーの場合は ピストンが動く高低差です 面積×高さ」がシリンダーの 体積であることを考えると 仕事の式は 圧力×系の体積変化」と 定義できます しかし 体積が増えて ピストンが 下に押し下げられるので 実際には周囲に 仕事をしていることになり 数値上は負の値になります したがって 仕事とは 圧力P×デルタV」の負の値 つまり膨張中に 発生した最終体積と 初期体積の変化と 定義されます 圧力-体積の仕事の単位は 通常 リッター-大気と 定義されます この単位は 従来のエネルギーの単位である ジュールに変換することができ 変換係数を使用すると 1リットルの大気は 101.3ジュールに相当します

<ol>
	<li>「準静的不可逆的プロセスの観点から、外部圧力と熱力学なしでの拡張作業」 Journal of Chemical Education 91、no. 3 (2014): 402-409.</li>
	<li>Gislason, Eric A., and Norman C. Craig. "General definitions of work and heat in thermodynamic processes." Journal of Chemical Education 64, no. 8 (1987): 660.</li>
	<li>「断熱変化:圧力体積の仕事のみを含む可逆的および不可逆的な変化」 Journal of Chemical Education 30, no. 4 (1953): 190. 
	 </li>
</ol>

運動の定量化

システムが変化すると、内部のエネルギーが変化し、システムから周囲、または周囲からシステムにエネルギーを移すことができます。  
 
 熱と仕事によってエネルギーが伝達されます。 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/795/795_Equations-01.png" style="height: 40px;" />
 
 熱が観測された温度変化の関数であるのに対し、仕事は圧力-体積の仕事と呼ばれる観測された体積変化の関数です。 仕事（ w ）は、ある距離（ D ）を通る力（F ）として定義できます。 
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/795/Equations-02.png" style="height: 40px;" />
 
 圧力 - 体積の仕事（または膨張の仕事）は、システムが拘束圧力に反して周囲を押し戻すか、周囲がシステムを圧縮するときに発生します。 この例は、内燃エンジンの作動中に発生します。 ガソリンと酸素の燃焼反応は発熱します。 このエネルギーの一部は熱として放出され、一部はシリンダ内の気体を膨張させてピストンを外側に押すことで、仕事として実行されます。 反応に関与している物質がシステムであり、エンジンや残りの宇宙が周囲です。 システムは、熱と周囲の仕事の両方によってエネルギーを失い、内部エネルギーが減少します。 
 
 シリンダの体積が増加すると（気体が膨張するなど）、外部の力に抗って押されます。これが単位面積あたりの力として定義された圧力です。 
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/795/795_Equations-03.png" style="height: 40px;" />
 
 方程式 2 と 3 から： 
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/795/795_Equations-04.png" style="height: 40px;" />
 
 面積と距離（ A × D ）の積は、シリンダ内のガスの体積の変化（ Δ V ）と等しくなります。 
 
 したがって、 
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/795/795_Equations-05.png" style="height: 40px;" />
 
 膨張中に体積が増加するため、 Vfinal > Vinitial 、および Δ V は正の値になります。 ただし、正の膨張（つまり、システムが周囲で仕事する場合）では、 w は負である必要があるため、負の符号が関係式に追加されます。  
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/795/795_Equations-06.png" style="height: 40px;" />
 
 この方程式によると、圧力 - 体積の仕事は、外圧（または対向圧）のマイナスに体積変化を掛けた値です。  
 
 この方程式に基づく仕事の単位は L·atm です。 その他の便利な変換係数は次のとおりです。  
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/795/795_Equations-07.png" style="height: 40px;" />
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/795/795_Equations-08.png" style="height: 40px;" />
 
 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: Endalpy から引用</a>しています。

システムが変化すると、その内部エネルギーが変化し、システムから周囲にエネルギーが伝達される可能性があります。

Education

JoVE Core

化学

Thermochemistry

熱化学

KEY TERMS AND CONCEPTS

主要用語と概念

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 called expansion work, happens when a system pushes against a restraining pressure. It can also happen when the surroundings compress the system.

A common example is an internal combustion engine. The combustion of gasoline and oxygen is exothermic, so it gives off energy. Some of that energy is released as heat, and some is used as work that expands the gases in the cylinder and pushes the piston outward. In this situation, the reacting substances are the system, and the engine and the rest of the universe are the surroundings. The system loses energy by heating and by doing work on the surroundings, so its internal energy decreases.

When a gas expands in a cylinder, it pushes against an external force. That force is pressure, which is force per unit area. The area of the piston times the distance it moves equals the change in gas volume, or ΔV. Since the volume increases during expansion, ΔV is positive.

For expansion, the work is written with a negative sign because the system is doing work on the surroundings. Pressure-volume work is the negative of the external pressure multiplied by the change in volume. The unit of this work is L·atm, and it can be converted using other common unit factors.

Pressure-Volume Work in Chemistry

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, 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...

quantifying heat

Heat Transfer and Specific Heat

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quantifying work

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

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thermochemical equations

Heat Changes in Chemical Equations

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constant pressure calorimetry

Coffee Cup Calorimeter Heat Changes

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constant volume calorimetry

Bomb Calorimeter Heat Measurement

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hess's law

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standard enthalpy of formation

Using Standard Enthalpy Values in Chemistry

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enthalpies of reaction

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key terms and concepts

Learn how pressure-volume work links gas expansion, internal energy, and sign conventions in chemistry, with an engine example and the L·atm unit.

Pressure-Volume Work in Chemistry | 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

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Physical Science

Energy And Waves

transfer-and-transformation-of-energy-including-work

Transfer and transformation of energy (including work)

Interactions Of Matter

Chemical reactions

Tennessee Academic Standards

High School

Physics

PHYS.PS3.7

Virginia  Standards of Learning

HIgh School

CH.7

CH.7.a

Texas Essential Knowledge and Skills

CHEM.13

CHEM.13.A

CHEM.13.C

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Energy

HS-PS3-3.

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physical-and-chemical-properties-of-matter

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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

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Chemical changes and their accompanying ...

First Law of Thermodynamics

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Hess's Law

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PS.Chm.7.3

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

Pressure-Volume Work in Chemistry

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