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

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Energy

PS.Chm.7.2

Quantifying Work

Bir sistemin iç enerjisinin ısı ve işin toplamı olarak tanımlandığını hatırlayalım. Isı kalorimetre kullanılarak ölçülürken, iş nasıl ölçülür? İş, bir nesnenin bir mesafe boyunca maruz kaldığı bir kuvvetin sonucudur.Bu nedenle iş kuvvet çarpı mesafeye eşittir. Bir golf sopası bir topa vurarak 100 metre fırlatırsa, iş yapmıştır. Golf sopasından topa enerji aktarılır.Bu durumda top, çevrenin iş yaptığı sistemdir. Kimyasal reaksiyonlarda iş, bir sistemdeki birden çok fiziksel veya kimyasal değişiklikle ilişkilendirilebilir. Yaygın olarak karşılaşılan bir iş türü, basınç-hacim işidir.Bir motorun silindirindeki yanmayı düşünelim. Yanma sadece ısı üretmekle kalmaz, aynı zamanda işi yapan gaz basıncını da üretir. Silindirdeki gaz hacmi genişlediğinde, basınç, çevredeki dış kuvvetlere karşı hareket ederek pistonu aşağı doğru iter.Basınç, bir alana etki eden bir kuvvet olarak tanımlanır. Burada, genleşen gazlardan gelen kuvvet, piston tabanının alanına dağıtılır. Başka bir deyişle, kuvvet basınç çarpı alandır.Böylece kuvvet çarpı mesafe olan iş, etki ettiği alan ve mesafe ile çarpılan basınç olarak yeniden yazılabilir. Motor silindiri için bu, pistonun hareket ettiği yükseklik farkıdır. Alan çarpı yüksekliğin bir silindirin hacmi olduğu göz önüne alındığında, iş için denklem, sistemin hacim değişimi çarpı basınç olarak tanımlanabilir.Bununla birlikte, hacim arttığı ve piston aşağıya doğru itildiği için, sistem aslında, çevre üzerinde iş yapar ve bu negatif bir değerdir. Bu nedenle iş, basıncın negatifi P çarpı delta V veya genleşme sırasında meydana gelen son ve ilk hacimdeki değişiklik olarak tanımlanır. Basınç-hacim işi birimi genellikle litre-atmosfer olarak tanımlanır.Bu birim, bir litre atmosfer 101, 3 Joule'e eşit olan dönüştürme faktörü kullanılarak geleneksel enerji birimi Joule'e dönüştürülebilir.

<ol>
	<li>Schmidt-Rohr, Klaus. "Yarı statik geri dönüşü olmayan süreçler açısından dış basınç ve termodinamik olmadan genleşme çalışması." Kimya Eğitimi Dergisi 91, no. 3 (2014): 402-409.</li>
	<li>Gislason, Eric A. ve Norman C. Craig. "Termodinamik süreçlerde iş ve ısının genel tanımları." Kimya Eğitimi Dergisi 64, no. 8 (1987): 660.</li>
	<li>O'Loane, J. Kenneth. "Adyabatik değişiklikler: Yalnızca basınç-hacim işini içeren tersinir ve geri dönüşü olmayan değişiklikler." Kimya Eğitimi Dergisi 30, no. 4 (1953): 190. 
	 </li>
</ol>

İş Ölçümü

Bir sistem değiştikçe iç enerjisi değişebilir ve enerji sistemden çevreye veya çevreden sisteme aktarılabilir. 
 
 Enerji transferi ısı ve iş yoluyla gerçekleşir. İç enerji, ısı ve iş arasındaki ilişki denklemle temsil edilir:
 
 <img alt=""Eq1"" src=""https://www.jovecore.com/CDNSource/lessons/795/795_Equations-01.png"" style=""height: 40px;"" />
 
 Isı, gözlemlenen bir sıcaklık değişiminin bir fonksiyonu iken, iş, basınç-hacim işi adı verilen gözlemlenen hacim değişikliğinin bir fonksiyonudur. İş (w), bir mesafe (D) boyunca etki eden bir kuvvet (F) olarak tanımlanabilir.
 
 <img alt=""Eq1"" src=""https://www.jovecore.com/CDNSource/lessons/795/Equations-02.png"" style=""height: 40px;"" />
 
 Basınç-hacim işi (veya genişletme işi), bir sistem çevreyi kısıtlayıcı bir basınca karşı geri ittiğinde veya çevre sistemi sıkıştırdığında meydana gelir. Bunun bir örneği, içten yanmalı bir motorun çalışması sırasında ortaya çıkar. Benzin ve oksijenin yanma reaksiyonu ekzotermiktir. Bu enerjinin bir kısmı ısı olarak verilir, bir kısmı da silindirdeki gazları genişleterek pistonu dışarı doğru iterek iş olarak gerçekleştirilir. Reaksiyona dahil olan maddeler sistemdir ve motor ve evrenin geri kalanı ise çevredir. Sistem hem ısıtarak hem de çevre üzerinde çalışarak enerji kaybeder ve iç enerjisi azalır.
 
 Bir silindirin hacmi arttığında (yani gaz genişlediğinde), birim alan başına kuvvet olarak tanımlanan basınç harici bir kuvvete karşı iter.
 
 <img alt=""Eq1"" src=""https://www.jovecore.com/CDNSource/lessons/795/795_Equations-03.png"" style=""height: 40px;"" />
 
 Denklem 2 ve 3'ten:
 
 <img alt=""Eq1"" src=""https://www.jovecore.com/CDNSource/lessons/795/795_Equations-04.png"" style=""height: 40px;"" />
 
 Alan ve mesafenin çarpımı (A × D) , silindirdeki gazın hacmindeki (ΔV) değişime eşittir.
 
 Bu nedenle,
 
 <img alt=""Eq1"" src=""https://www.jovecore.com/CDNSource/lessons/795/795_Equations-05.png"" style=""height: 40px;"" />
 
 Genişleme sırasında hacim arttığından, Vfinal > Vinitial ve ΔV pozitiftir. Bununla birlikte, pozitif bir genişleme için (yani, sistem çevre üzerinde iş yaptığında), w negatif olmalıdır ve bu nedenle denkleme negatif işaret eklenir. 
 
 <img alt=""Eq1"" src=""https://www.jovecore.com/CDNSource/lessons/795/795_Equations-06.png"" style=""height: 40px;"" />
 
 Bu denkleme göre, basınç-hacim işi, dış basıncın (veya karşıt basıncın) hacimdeki değişimle çarpımı sonucu negatiftir. 
 
 Bu denkleme dayalı iş birimi L·atm'dir. Diğer bazı yararlı dönüştürme faktörleri şunlardır: 
 
 <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;"" />
 
 Bu metin bu kaynaktan uyarlanmıştır: <a href=""https://openstax.org/books/chemistry-2e/pages/5-3-enthalpy"">Openstax, Chemistry 2e, Section 5.3: Enthalpy</a>.

Bir sistem bir değişime uğradıkça, iç enerjisi değişebilir ve enerji sistemden çevreye aktarılabilir veya sistemden çevreye aktarılabilir.

Education

JoVE Core

Kimya

Thermochemistry

Termokimya

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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...

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internal energy

Internal Energy, Heat, and Work

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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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constant pressure calorimetry

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constant volume calorimetry

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standard enthalpy of formation

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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

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 Kimya, özlü ve kolay anlaşılır animasyon video derslerini kullanarak genel kimya kavramlarına hayat veriyor. Ek olarak, bilim insanı uygulama videolarımız ile klasik ve orijinal araştırma deneylerini dünya çapında günümüz laboratuvarlarında görselleştiriyoruz.

Matter and its Interactions

PS.Chm.4.1

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Ohio’s Learning Standards and Model Curriculum

Physical Science

Energy And Waves

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Transfer and transformation of energy (including work)

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Chemical reactions

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High School

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HIgh School

CH.7

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CHEM.13.C

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New York State Science Learning Standards

HS. Energy

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Classifying Matter by State

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Classifying Matter by Composition

Matter: Pure Substances and Mixtures
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PS.Chm.7.1

Energy Basics

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	Determining the Mass of the Unknown LiquidExpand
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Use mathematics and computational thinking to explain the relationships among pressure, temperature, volume, and quantity of gas, both qualitatively and quantitatively.

PS.Chm.7.3

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

Pressure-Volume Work in Chemistry

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