Name: internal energy, heat, and work
Uploaded: 2020-09-03T13:38:27.000Z
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K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Energy

PS.Chm.7.2

Internal Energy

В химическом процессе разница между внутренней энергией реагентов и продуктов, обозначеная дельта U, используется для определения получила или потеряла энергию система во время реакции. Если дельта U больше нуля, конечная внутренняя энергия была выше начальной внутренней энергии, и система приобрела энергию во время реакции. Если дельта U меньше нуля, конечная внутренняя энергия ниже начальной внутренней энергии, то есть, система потеряла энергию.Согласно первому закону термодинамики, любое изменение энергии системы должно уравновешиваться равным и противоположным изменением вокруг системы. Таким образом, изменение внутренней энергии системы равно энергии, передаваемой в виде тепла, обозначенной q"плюс энергия, передаваемая как работа, обозначенная w"во время процесса. В химии знаки тепла и работы зависят от того, получает ли система энергию, или теряет.Рассмотрим превращение углекислого газа в элементы углерод и кислород. Реагент имеет более низкую внутреннюю энергию, чем продукты, что означает, что дельта U положительно. Энергия передается из окружающей среды системе, увеличивая ее внутреннюю энергию.Как вариант, во время реакции между серой и газообразным кислородом для получения диоксида серы, энергия передается окружающей среде. Здесь продукты имеют более низкую внутреннюю энергию чем реагенты, а дельта U отрицательно. Следовательно, дельта U зависит только от начального и конечного внутреннего энергетического состояния системы и количества тепла и работы которым она обменивается с окружающей средой.

Внутренняя энергия

Суммарное количество всех возможных видов энергии, присутствующих в веществе, называется внутренней энергией (U), иногда представляет собой символы E. Предположим, что система с начальной внутренней энергией, Уинициал, претерпевает изменения в энергии (перенос работы или тепла), а конечная внутренняя энергия системы является UFinal. Изменение внутренней энергии равно разнице между UFinal и UInitial.  
 
 <img alt=""Eq1"" src=""https://www.jove.com/files/core/CDNSource/lessons/793/793_Equations-01.png"" style=""height: 40px;"" />
 
 Хотя значения для UFinal и Uinial не могут быть определены для системы, первый закон термодинамики требует только значения ΔU, которое можно определить даже без знания значений UFinal  и Uinial. Положительное значение ΔU дает результат, когда UFinal > Uinitial, и указывает, что система получила энергию от окружающей среды. Отрицательное значение ΔU достигается, когда UFinal < Uinial, и указывает на то, что система потеряла энергию в окружающую среду. 
 
 Тепло (тепловая энергия) и работа (механическая энергия) - это два различных способа обмена энергии системой с окружающей средой. Энергия передается в систему, когда она поглощает тепло (q) из окружающей среды или когда окружающая среда работает (w) в системе.  
 
 Например, энергия передается в металлическую проволоку комнатной температуры, если она погружена в горячую воду (проволока поглощает тепло из воды), или когда провод быстро согнут вперед-назад (проволока нагревается из-за работы с ней). Оба процесса увеличивают внутреннюю энергию провода, что отражается в повышении температуры провода. И наоборот, энергия передается из системы при потере тепла из системы или при работе системы в условиях окружающей среды. Например, сжигание ракетного топлива выделяет огромное количество тепла, а также выполняет работы на окрестности, прикладывая усилие на расстоянии (в результате чего космический челнок поднимается с земли). Оба процесса уменьшают внутреннюю энергию системы. 
 
 Взаимосвязь между внутренней энергией, теплом и работой может быть представлена уравнением: 
 
 <img alt=""Eq1"" src=""https://www.jove.com/files/core/CDNSource/lessons/793/793_Equations-02.png"" style=""height: 40px;"" />
 
 Это одна из версий первого закона термодинамики, и она показывает, что внутренняя энергия системы изменяется за счет потока тепла в систему или из нее, или работа выполняется системой или системой. Признаки нагрева и работы зависят от того, получает ли система энергию или теряет ее. Положительный q - это поток тепла в систему из окружающей среды, а отрицательный q - это поток тепла из системы. Работа, w, является положительной, если она выполняется над системе, и отрицательной, если она выполняется системой. 
 
 Когда q и w одновременно положительны (>0), ΔU всегда положительны (>0), и внутренняя энергия системы увеличивается. Если значения q и w являются отрицательными (<0), то значение ΔU всегда отрицательное (<0), а внутренняя энергия системы уменьшается. Если q и w имеют разные условные обозначения знаков, то знак ΔU зависит от относительных величин q и W   
 
 Единица СИ энергии, тепла и работы — джоуль (J). 
 
 Этот текст был адаптирован из<a href=""https://openstax.org/books/chemistry-2e/pages/5-3-enthalpy"">OpenStax Химия 2е изд., раздел 5.3: Энтальпия</a>. "

Совокупность всех возможных видов энергии, присутствующих в веществе, называется внутренней энергией (U), иногда обозначаемой как E. Предположим, что система с ...

Education

JoVE Core

Химия

Один

Thermochemistry

Термохимия

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

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...

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enthalpy

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thermochemical equations

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constant volume calorimetry

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hess's law

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standard enthalpy of formation

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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

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Matter and its Interactions

PS.Chm.4.1

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Ohio’s Learning Standards and Model Curriculum

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PS.Chm.7.3

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Internal Energy, Heat, and Work

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