Name: combustion heat and hydrocarbon stability
Uploaded: 2025-05-22T09:05:33.000Z
Duration: 2 min 12 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.8

IPC.8.A

Enthalpy and Heat of Reaction

Kısaltılmış H olan entalpi, E veya U olarak kısaltılan iç enerjinin toplamına ve basınç ve hacmin çarpımına eşittir.
Entalpideki değişim, ΔH, ürünlerin entalpileri ile reaktanlar arasındaki fark olarak ifade edilir. Sabit sıcaklık ve basınçta, ΔH, sistem ile çevre arasında değiş tokuş edilen ısı enerjisi miktarına veya reaksiyonun ısısına eşittir.
ΔH pozitif olduğunda, reaksiyonlar ısıyı emer ve endotermiktir. ΔH negatifse, reaksiyonlar ısıyı serbest bırakır ve ekzotermiktir.
Yanma, bir maddenin atmosferik oksijen gibi bir oksidan varlığında yanarak ısı şeklinde enerji açığa çıkardığı ekzotermik bir süreç örneğidir.
Açığa çıkan ısı, bir maddenin bir molünün yakılmasıyla salınan ısı enerjisi miktarı olan molar yanma ısısı olarak ölçülür.
Bir hidrokarbon yandığında, yakıttan gelen karbon ve hidrojen, enerji salınımı ile birlikte su ve karbondioksit üretmek için moleküler oksijenle birleşir.
Bir hidrokarbon için yanma ısısının değeri, zincirdeki karbon atomlarının sayısı ile artar, çünkü yanma için daha fazla karbon bulunur ve daha fazla bağ değişikliğe uğrar.
Örneğin, tek karbonlu bir bileşik olan metanın yanması, dört karbon atomuna sahip olan bütanınkinden daha az ısı enerjisi üretir.
Yanma ısısı, aynı moleküler formüle ancak farklı yapılara sahip hidrokarbonların nispi stabilitesini belirlemenin kritik bir yoludur.
Oktan, 2-metilheptan ve 2,2-dimetilhekzanın yanma ısılarını düşünün.
Bu bileşikler aynı sayıda karbon atomuna sahiptir, ancak metil grupları her molekülde farklı konumlarda bağlanır.
Oktan en büyük yanma ısısına sahiptir. Dallanma arttıkça ΔH azalır, bu da dallanmanın bir hidrokarbonun stabilitesini artırdığını düşündürür.

entalpi ve reaksiyon isısı

Genellikle yanma olarak bilinen yanma, bir maddenin çoğu durumda moleküler oksijen olan oksitleyici bir maddeyle reaksiyona girerek ısı, ışık veya ses biçiminde enerji açığa çıkardığı bir reaksiyondur. Yanma ısısına yanma entalpisi de denir. Bir mol maddenin sabit basınçta tamamen yanması sırasında açığa çıkan enerjiye molar yanma ısısı denir. Yanma reaksiyonları ekzotermiktir; yani enerji açığa çıkarırlar ve ΔH işaret kuralları negatiftir.

1772'de Fransız kimyager Antoine Lavoisier, yanmış kükürt ürünlerinin, reaktantın başlangıç ​​kütlesinden daha ağır olduğunu keşfetti. Kükürtün hava ile birleşerek ağırlığın artmasına neden olduğunu öne sürdü. Daha sonra Joseph Priestley'in 1774'te havanın bir bileşeni olarak "oksijen"i keşfetmesi, Lavoisier'i kükürtün havadaki oksijenle birleşerek kütlesinin artmasına yol açtığına inandırdı. Yanmanın oksijenle birleşme anlamına geldiği sonucuna vardı. Başka bir deyişle kükürt yandı.

Yanma reaksiyonlarının örnekleri arasında doğal gaz ve kömür gibi hidrokarbon yakıtların yakılması yer alır. Hidrokarbonları içeren yanma reaksiyonlarında açığa çıkan enerji miktarı, yanmaya giren yakıtın türüne bağlı olarak değişir.

Örneğin doğalgazın yanması metanın (CH4) verdiği reaksiyon:

<img alt="Eq2" src="/files/ftp_upload/11692/11692_Reaction%20Equation-Combustion%20of%20Methane.svg" style="text-align: center; height: 18px;">

reaksiyonla verilen bütanınkinden (C4H10) daha az ısı enerjisi üretir:

<img alt="Eq1" src="/files/ftp_upload/11692/11692_Reaction%20Equation-Combustion%20of%20Butane.svg" style="text-align: center; height: 17.5px;">

Bu nedenle, hidrokarbonu yakmak için gereken oksijen moleküllerinin sayısı ve oluşan her ürünün molekül sayısı, hidrokarbonun bileşimine bağlıdır.

Yanma ısısı, dallanmış hidrokarbonların göreceli stabilitesini aynı moleküler formülle yönetir. Yapıdaki farklılık, hidrokarbon zinciri boyunca farklı pozisyonlara bağlanan metil gruplarından kaynaklanmaktadır. Açığa çıkan ısı enerjisi miktarı, dallanmanın artması ile azalır; burada oldukça dallanmış 2,2-dimetil hekzan, oktan ile karşılaştırıldığında daha düşük enerji üretir. Bu nedenle dallanmamış oktan, dallanmış muadilinden daha az kararlıdır.

Entalpi ve Reaksiyon Isısı

Yaygın olarak yanma olarak bilinen yanma, bir maddenin çoğu durumda moleküler oksijen olan bir oksitleyici madde ile reaksiyona girdiği bir reaksiyondur ...

Education

JoVE Core

Organic Chemistry

Organik Kimya

Unit 1

Ünite 1

Thermodynamics and Chemical Kinetics

Termodinamik ve Kimyasal Kinetik

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

combustion heat and hydrocarbon stability

Combustion is a burning reaction that releases energy as heat, light, or sound. It happens when a substance reacts with an oxidizing agent, usually molecular oxygen. The heat of combustion is also called the enthalpy of combustion. The energy released when one mole of a substance undergoes complete combustion at constant pressure is the molar heat of combustion.

Combustion reactions are exothermic, so they give off energy. For that reason, the sign of ΔH is negative. In 1772, Antoine Lavoisier found that burned sulfur products weighed more than the original sulfur. He suggested that sulfur combined with air. After Joseph Priestley identified oxygen in 1774, Lavoisier concluded that sulfur combined with oxygen in air. He therefore defined combustion as combining with oxygen.

Hydrocarbon fuels such as natural gas and coal also undergo combustion. The amount of energy released can change with the fuel. For example, methane (CH4) releases less heat energy than butane (C4H10). The number of oxygen molecules needed and the number of product molecules formed depend on the hydrocarbon’s composition.

The heat of combustion also helps explain the stability of branched hydrocarbons with the same molecular formula. Branching comes from methyl groups attached at different positions along the hydrocarbon chain. As branching increases, the amount of heat energy released decreases. For example, highly branched 2,2-dimethylhexane releases less energy than octane. This means unbranched octane is less stable than its branched form.

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enthalpy and heat of reaction

Combustion is a burning reaction that releases energy as heat, light, or sound. It happens when a substance reacts with an oxidizing agent, usually molecular oxygen. The heat of combustion is also called the enthalpy of combustion. The energy released when one mole of a substance undergoes complete combustion at constant pressure is the molar heat of combustion. Combustion reactions are exothermic, so they give off energy. For that reason, the sign of ΔH is negative. In 1772, Antoine Lavoisier...

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bond dissociation energy and activation energy

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key terms and concepts

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organic chemistry

JoVE Core Organik Kimya, kısa ve anlaşılması kolay animasyonlu video dersleri kullanarak stereokimya, reaksiyonlar ve mekanizmaların temel kavramlarını açıklar. Buna ek olarak, bilim insanlarının yer aldığı videolar, ilgili kavramların günümüz laboratuvarlarında gerçekleştirilen klasik ve orijinal araştırma deneylerinde nasıl uygulandığını göstermektedir.

Alabama Course of Study Science

9-12

Environmental Science

Earth and Human Activity

9-12.EVS.4.6

9-12.EVS.4.11.b

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IPC.8.D

Science concepts. The student knows that changes in matter affect everyday life. The student is expected to:

Combustion Heat and Hydrocarbon Stability

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