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

في العملية الكيميائية،الفرق بين الطاقات الداخلية للمواد المتفاعلة والنواتج،التي يمثلها ΔU،يستخدم لتحديد ما إذا كان النظام قد اكتسب أو فقد الطاقة أثناء التفاعل. إذا كانت ΔU أكبر من الصفر،فإن الطاقة الداخلية النهائية تكون أعلى من الطاقة الداخلية الأولية،و يكون النظام قد اكتسب الطاقة أثناء التفاعل. إذا كانت ΔU أقل من الصفر،فإن الطاقة الداخلية النهائية أقل من الطاقة الداخلية الأولية،وهذا يعني أن النظام فقد طاقة.وفقًا للقانون الأول للديناميكا الحرارية،يجب أن يحدث أي تغيير في طاقة النظام على أن يكون متوازناَمن خلال تغيير مساوي ومعاكس في محيطه. وبالتالي،التغيير في الطاقة الداخلية للنظام يساوي الطاقة المنقولة على شكل حرارة،التي يرمز لها بواسطة q"بالإضافة إلى الطاقة المنقولة كشغل،و يرمز لها بالحرف w"أثناء العملية. في الكيمياء،علامات الحرارة والشغل تعتمد على ما إذا كان النظام يكتسب أو يفقد الطاقة.لنضع في اعتبارنا،تحول ثاني أكسيد الكربون إلى عنصر الكربون والأكسجين. المتفاعل لديه طاقة داخلية أقل من الناتج،ما يعنى أن قيمة ΔU موجبة. يتم نقل الطاقة من البيئة المحيطة للنظام و زيادة طاقته الداخلية.بدلا من ذلك،أثناء التفاعل بين غاز الكبريت والأكسجين لإنتاج ثاني أكسيد الكبريت،يتم نقل الطاقة إلى المناطق المحيطة. هنا،النواتج لديها طاقة داخلية أقل من المتفاعلات،و ΔU سالبة. وبالتالي،تعتمد ΔU فقط على الحالة الأولية والنهائية للطاقة الداخلية للنظام،ومقدار الحرارة،والشغل التي تم تبادلها مع المحيط.

الطاقة الداخلية

يطلق على مجموع جميع أنواع الطاقة الممكنة الموجودة في مادة ما اسم الطاقة الداخلية (U)، التي يتم ترميزها في بعض الأحيان كـ E. افترض أن النظام ذي الطاقة الداخلية الأوليةUأولي، يخضع لتغيير في الطاقة (نقل للعمل أو للحرارة)، والطاقة الداخلية النهائية للنظام هي Uنهائي. التغير في الطاقة الداخلية يساوي الفرق بين Ufinal و Uinitial. <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/793/793_Equations-01.png" style="height: 40px;" /> بالرغم من أن قيم Uنهائي و Uأولي لا يمكن تحديدها لنظام ما، فإن القانون الأول الديناميكا الحرارية لا يتطلب سوى قيمة &دلتا;U، والتي يمكن تحديدها حتى بدون معرفة قيم Uنهائي و Uأولي. قيمة موجبة لـ &دلتا;U تنتج عندما Uنهائي > Uأولي ، وتشير إلى أن النظام قد اكتسب طاقة من البيئة المحيطة. يتم الحصول على قيمة سالبة لـ &دلتا;U عندما Uنهائي < Uأولي ، وهي تشير إلى أن النظام قد فقد الطاقة من البيئة المحيطة. الحرارة (الطاقة الحرارية) والعمل (الطاقة الميكانيكية) هما طريقتان مختلفتان يمكن للنظام تبادل الطاقة مع محيطه. يتم نقل الطاقة إلى نظام عندما يمتص الحرارة (q) من البيئة المحيطة أو عندما تعمل البيئة المحيطة (w) على النظام.  على سبيل المثال، يتم نقل الطاقة إلى سلك معدني بدرجة حرارة الغرفة إذا تم غمره في الماء الساخن (يمتص السلك الحرارة من الماء)، أو عندما يتم ثني السلك سريعاً للخلف وللأمام (يصبح السلك أكثر دفئاً بسبب العمل عليه). تعمل كلتا العمليتين على زيادة الطاقة الداخلية للسلك، وهو ما ينعكس في زيادة درجة حرارة السلك. على العكس من ذلك، يتم نقل الطاقة من النظام عند فقدان الحرارة من النظام أو عندما يعمل النظام في المناطق المحيطة. على سبيل المثال، يؤدي حرق وقود الصواريخ إلى إطلاق كمية هائلة من الحرارة وأيضاً يؤدي العمل على المناطق المحيطة من خلال تطبيق قوة على مسافة (مما يتسبب في انطلاق مكوك فضائي من الأرض). كلتا العمليتين تقلل الطاقة الداخلية للنظام. يمكن تمثيل العلاقة بين الطاقة الداخلية والحرارة والشغل بالمعادلة: <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/793/793_Equations-02.png" style="height: 40px;" /> هذه نسخة واحدة من القانون الأول للديناميكا الحرارية ، وهي توضح أن الطاقة الداخلية للنظام تتغير من خلال تدفق الحرارة داخل أو خارج النظام أو يتم العمل على النظام أو بواسطته. تعتمد علامات الحرارة والعمل على ما إذا كان النظام يكتسب أو يفقد الطاقة. يشير q الإيجابي إلى تدفق الحرارة إلى النظام من المناطق المحيطة، بينما يشير q السالب إلى تدفق الحرارة خارج النظام. يكون العمل، w ، موجباً إذا تم على النظام وسالب إذا تم بواسطة النظام. عندما تكون كل من q و w موجبة (>0)، تكون &دلتا;U موجبة دائماً (>0)، و تزداد الطاقة الداخلية للنظام. عندما يكون كل من q و w سالبين (<0)) ، تكون &دلتا;U سالبة دائماً (<0)) ، والطاقة الداخلية للنظام تنقص. إذا كان لكل من q و w اصطلاحات إشارات مختلفة ، فإن علامة &دلتا;U تعتمد على المقادير النسبية لـ q و w.     وحدة النظام الدولي للطاقة والحرارة والشغل هي الجول (J). هذا النص مقتبس من <a href="https://openstax.org/books/chemistry-2e/pages/5-3-enthalpy">OpenStax Chemistry 2e, Section 5.3: Enthalpy</a>.

يطلق على إجمالي جميع أنواع الطاقة الممكنة الموجودة في مادة ما الطاقة الداخلية (U) ، والتي يرمز إليها أحيانا باسم E. افترض نظاما يحتوي على ...

Education

JoVE Core

الكيمياء

واحد

Thermochemistry

الكيمياء الحرارية

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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 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

Physics

P-PS3-1

P-PS3-2

new-york-state-science-learning-standards

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

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Chemical changes and their accompanying ...

First Law of Thermodynamics

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Quantifying Heat

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Enthalpy

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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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PS.Chm.7.3

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

Internal Energy, Heat, and Work

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