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

화학적인 과정에서 반응물과 생성물의 내부 에너지 간의 차이, 즉, 델타 U를 사용하여 계가 반응하는 동안 에너지를 얻었는지 또는 잃었는지 여부를 판단합니다. ΔU가 0보다 크면 최종 내부 에너지가 초기 내부 에너지보다 높고 계는 반응하는 동안 에너지를 얻은 것입니다. ΔU가 0보다 작으면 최종 내부 에너지는 초기 내부 에너지보다 낮으며 이는 계의 에너지 손실을 의미합니다.

열역학 제1법칙에 따르면, 계에서 에너지의 어떤 변화도 주변 환경에서 크기가 같고 방향이 반대되는 에너지의 변화에 의해 균형을 이루어야 합니다. 따라서, 계의 내부 에너지의 변화는 프로세스 기간에 q"로 상징되는 열로 전달되는 에너지와 w"로 상징되는 일로 전달되는 에너지의 합과 동일합니다. 화학에서 열과 일의 음양은 계가 에너지를 얻는지 또는 잃는 지에 따라 달라집니다.

이산화탄소를 탄소 원소와 산소로 변환하는 과정을 고려해 봅시다. 반응물은 생성물보다 내부 에너지가 낮으며 그 결과 델타 U가 양수입니다. 에너지는 환경에서 계로 전달되어 내부 에너지를 증가시킵니다.

대신에 유황과 산소 기체가 반응하여 이산화황을 생성하는 동안 에너지는 주위 환경으로 전달됩니다. 여기서 생성물은 반응물보다 내부 에너지가 낮으며 결국 델타U는 음수입니다. 따라서 델타U는 계의 초기 및 최종 내부 에너지 상태와 환경과 교환하는 열 및 일의 규모에만 연관됩니다.

내부 에너지

물질에 존재하는 가능한 모든 종류의 에너지의 총합을 내부 에너지(U)라고 하며, 때로는 E로 기호화되기도 합니다. 초기 내부 에너지인 U_initial을 갖는 계가 에너지 변화(일 또는 열 전달)를 겪는다고 가정합니다. 시스템의 최종 내부 에너지는 U_final입니다. 내부 에너지의 변화는 U_final과 U_initial의 차이와 같습니다.

<img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/793/793_Equations-01.png" style="height: 40px;" />

시스템에서는 U_final과 U_initial의 값을 결정할 수 없지만, 열역학 제1법칙에서는 ΔU의 값만 필요하며, U_final과 U_initial의 값을 몰라도 U_final과 U_initial의 값을 결정할 수 있습니다. ΔU의 양수 값은 U_final > U_initial일 때 발생하며 시스템이 주변으로부터 에너지를 얻었음을 나타냅니다. ΔU의 음수 값은 U_final < U_initial일 때 얻어지며, 이는 시스템이 주변으로 에너지를 손실했음을 나타냅니다.

열(열 에너지)과 일(기계 에너지)은 시스템이 주변 환경과 에너지를 교환할 수 있는 두 가지 서로 다른 방식입니다. 시스템이 주변으로부터 열(q)을 흡수하거나 주변이 시스템에 일(w)할 때 에너지가 시스템으로 전달됩니다.

예를 들어, 상온의 금속선을 뜨거운 물에 담그거나(선이 물에서 열을 흡수함), 선을 앞뒤로 빠르게 구부리면(선이 하는 일로 인해 선이 따뜻해짐) 에너지가 상온의 금속선으로 전달됩니다. 두 공정 모두 와이어의 내부 에너지를 증가시키며 이는 와이어 온도의 증가에 반영됩니다. 반대로, 시스템에서 열이 손실되거나 시스템이 주변 환경에서 작동할 때 에너지는 시스템 외부로 전달됩니다. 예를 들어, 로켓 연료가 연소되면 엄청난 양의 열이 방출되고, 먼 거리에 걸쳐 힘을 가하여 주변에 일을 수행합니다(우주 왕복선이 지상에서 이륙하게 됨). 두 프로세스 모두 시스템의 내부 에너지를 감소시킵니다.

내부 에너지, 열, 일의 관계는 다음 방정식으로 나타낼 수 있습니다.

<img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/793/793_Equations-02.png" style="height: 40px;" />

이것은 열역학 제1법칙의 한 버전으로, 시스템 안팎으로의 열 흐름을 통해 시스템의 내부 에너지가 변화하거나 시스템에서 또는 시스템에 의해 작업이 수행됨을 보여줍니다. 열과 일의 징후는 시스템이 에너지를 얻거나 잃는 여부에 따라 달라집니다. 양의 q는 주변에서 시스템으로의 열 흐름이고, 음의 q는 시스템에서 나가는 열 흐름입니다. 일 w는 시스템에서 수행되면 양수이고 시스템에서 수행되면 음수입니다.

q와 w가 모두 양수(>0)이면 ΔU는 항상 양수(>0)이고 시스템의 내부 에너지가 증가합니다. q와 w가 모두 음수(<0)이면 ΔU는 항상 음수(<0)이고 시스템의 내부 에너지는 감소합니다. q와 w가 서로 다른 부호 규칙을 갖는 경우 ΔU의 부호는 q와 w의 상대적 크기에 따라 달라집니다.

에너지, 열, 일의 SI 단위는 줄(J)입니다.

이 문서는 에서 발췌되었습니다 <a href="https://openstax.org/books/chemistry-2e/pages/5-3-enthalpy">OpenStax Chemistry 2e, Section 5.3: Enthalpy</a>.

물질에 존재하는 모든 가능한 종류의 에너지의 총합을 내부 에너지(U)라고 하며 때로는 E로 기호화됩니다.

Education

교육

JoVE Core

화학

하나

Thermochemistry

열화학

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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

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hess's law

Calculating Reaction Heat with 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

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 화학은 간결하고 이해하기 쉬운 애니메이션을 통해 일반 화학 개념을 설명합니다. 또한, 과학자가 직접 고전실험과 연구실험을 진행하는 실사 영상을 제공합니다.

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

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CH.7

CH.7.a

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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

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South Carolina College and Career Ready Science Standards

Physics

P-PS3-1

P-PS3-2

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New York State Science Learning Standards

HS. Energy

HS-PS3-1.

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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

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

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Quantifying Heat

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Quantifying Work

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Enthalpy

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Thermochemical Equations

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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 ...

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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

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Standard Enthalpy of Formation

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Enthalpies of Reaction

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PS.Chm.7.3

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

Internal Energy, Heat, and Work

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