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

In een chemisch proces wordt het verschil tussen de interne energieën van reactanten en producten, weergegeven door ΔU, gebruikt om te bepalen of het systeem energie heeft gewonnen of verloren tijdens de reactie. Als ΔU groter is dan nul, was de uiteindelijke inwendige energie hoger dan de initiële inwendige energie en won het systeem energie tijdens de reactie. Als ΔU kleiner is dan nul, is de uiteindelijke innwendige energie lager dan de initiële inwendige energie, wat betekent dat het systeem energie heeft verloren.Volgens de eerste wet van de thermodynamica moet elke verandering in de energie van een systeem worden gecompenseerd door een gelijke en tegengestelde verandering in zijn omgeving. De verandering in de inwendige energie van een systeem is dus gelijk aan de energie die wordt overgedragen als warmte, gesymboliseerd door q"plus de energie die wordt overgedragen als arbeid, gesymboliseerd door w"tijdens het proces. In de scheikunde hangen de signalen voor warmte en arbeid af van het feit of het systeem energie wint of verliest.Denk aan de omzetting van kooldioxide in elementaire koolstof en zuurstof. De reactant heeft een lagere inwendige energie dan de producten, wat betekent dat ΔU positief is. Energie wordt overgedragen van de omgeving naar het systeem waardoor de inwendige energie toeneemt.Als alternatief wordt tijdens de reactie tussen zwavel en zuurstofgas om zwaveldioxide te maken, energie overgedragen naar de omgeving. Hier hebben de producten een lagere inwendige energie dan de reactanten, en ΔU is negatief. Daarom hangt ΔU alleen af van de initiële en uiteindelijke inwendige energietoestanden van het systeem en de omvang van warmte en arbeid die wordt uitgewisseld met de omgeving.

interne energie

Het totaal van alle mogelijke soorten energie die in een substantie aanwezig zijn, wordt de interne energie (U) genoemd, soms gesymboliseerd als E. Stel dat een systeem met initiële interne energie, Uinitial, een verandering in energie ondergaat (overdracht van werk of warmte), en de uiteindelijke interne energie van het systeem is Ufinal. Verandering in interne energie is gelijk aan het verschil tussen Ufinal en Uinitial. <img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/793/793_Equations-01.png" style="height: 40px;"> Hoewel de waarden voor Ufinal en Uinitial niet voor een systeem kunnen worden bepaald, vereist de eerste wet van de thermodynamica alleen de waarde van ΔU, die zelfs kan worden bepaald zonder de waarden van Ufinal en Uinitial te kennen. Een positieve waarde van ΔU ontstaat wanneer Ufinal > Uinitial, en geeft aan dat het systeem energie uit de omgeving heeft gewonnen. Een negatieve waarde van ΔU wordt verkregen wanneer Ufinal < Uinitial, en geeft aan dat het systeem energie aan de omgeving heeft verloren. Warmte (thermische energie) en arbeid (mechanische energie) zijn de twee verschillende manieren waarop een systeem energie kan uitwisselen met zijn omgeving. Energie wordt in een systeem overgedragen wanneer het warmte (q) uit de omgeving absorbeert of wanneer de omgeving op het systeem werkt (w). Er wordt bijvoorbeeld energie overgebracht naar metaaldraad op kamertemperatuur als deze wordt ondergedompeld in heet water (de draad absorbeert warmte uit het water), of wanneer de draad snel heen en weer wordt gebogen (de draad wordt warmer vanwege de werkzaamheden die aan de draad worden verricht). Beide processen verhogen de interne energie van de draad, wat tot uiting komt in een stijging van de temperatuur van de draad. Omgekeerd wordt energie uit een systeem overgedragen wanneer warmte uit het systeem verloren gaat of wanneer het systeem op de omgeving inwerkt. Bij de verbranding van raketbrandstof komt bijvoorbeeld een enorme hoeveelheid warmte vrij en wordt ook arbeid op de omgeving uitgeoefend door over een afstand een kracht uit te oefenen (waardoor een space shuttle van de grond opstijgt). Beide processen verminderen de interne energie van het systeem. De relatie tussen interne energie, warmte en arbeid kan worden weergegeven door de vergelijking: <img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/793/793_Equations-02.png" style="height: 40px;"> Dit is één versie van de eerste wet van de thermodynamica, en deze laat zien dat de interne energie van een systeem verandert door de warmtestroom in of uit het systeem of door werk dat op of door het systeem wordt verricht. De signalen voor warmte en werk zijn afhankelijk van de vraag of het systeem energie wint of verliest. Positieve q is de warmtestroom die vanuit de omgeving het systeem binnenkomt, terwijl negatieve q de warmtestroom uit het systeem is. Het werk, w, is positief als het op het systeem wordt gedaan en negatief als het door het systeem wordt gedaan. Wanneer q en w beide positief zijn (>0), is ΔU altijd positief (>0) en neemt de interne energie van het systeem toe. Wanneer q en w beide negatief zijn (<0), is ΔU altijd negatief (<0) en neemt de interne energie van het systeem af. Als q en w verschillende tekenconventies hebben, hangt het teken van ΔU af van de relatieve grootheden van q en w. De SI-eenheid van energie, warmte en arbeid is joule (J). Dit tekst is aangepast van <a href="https://openstax.org/books/chemistry-2e/pages/5-3-enthalpy">OpenStax Chemistry 2e, Sectie 5.3: Enthalpie</a>.

Interne energie

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 ...

Education

JoVE Core

Scheikunde

Eén

Thermochemistry

Thermochemie

KEY TERMS AND CONCEPTS

BELANGRIJKE TERMEN EN CONCEPTEN

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

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constant pressure calorimetry

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constant volume calorimetry

Bomb Calorimeter Heat Measurement

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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

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 Chemistry brings general chemistry concepts to life using concise and easy-to-understand animated video lessons. Plus, in the scientist-in-action videos, we demonstrate classical and original research experiments performed in today's laboratories worldwide.

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

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P-PS3-2

new-york-state-science-learning-standards

New York State Science Learning Standards

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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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