Name: boiling point and vapor pressure
Uploaded: 2020-03-26T07:22:27.000Z
Duration: 4 min 25 s
Channel: JoVE

K12 Standards

Georgia Standards of Excellence

9-12

Physical Science

SPS2.

Physical Properties

Boiling Points

Sıvılar, molekülleri arasındaki zayıf etkileşimlerle bir arada tutulur. Gaz fazına geçmek için, bir molekülün bu etkileşimlerin üstesinden gelmek için ısıdan veya diğer kaynaklardan yeterli enerji kazanması gerekir.
Oda sıcaklığında saf bir sıvının kapalı bir kabını düşünelim. Yüzeydeki sıvı faz moleküllerinin bir kısmı buharlaşmak için yeterli enerji kazanır ve bu buharın bir kısmı enerji kaybeder ve tekrar sıvıya yoğunlaşır. Buharlaşma ve yoğuşma oranları aynı olduğunda, sıvı ve buhar dengeye ulaşır. Bu noktada, sıvının üzerindeki boşluk buharla doyurulur ve kap içindeki sıvı ve buhar miktarında net bir değişiklik olmaz. Buharın uyguladığı basınca buhar basıncı denir.
Şimdi, açık bir sıvı kabı düşünün. Burada buhar dışarı çıkabilir ve sıvının üzerindeki alanın doymasını önleyebilir. Böylece, sıvı kalmayana kadar buharlaşma devam edebilir. Bir sıvının sıcaklığı arttıkça buharlaşma hızı da artar ve dolayısıyla buhar basıncı da artar. Yeterli ısı eklenirse, sıvının daha derinlerindeki moleküller buharlaşmaya başlar ve bu da buhar kabarcıkları oluşumu olarak görürüz.
Buna kaynama denir ve bileşiğin buhar basıncı atmosfer basıncına eşit olduğunda başlar. Bunun meydana geldiği sıcaklık kaynama noktasıdır. Her saf madde, moleküller arası etkileşimlerin farklı türlerine ve güçlerine sahip olduğundan, farklı maddelerin farklı kaynama noktaları vardır.
Şimdi, moleküller arası etkileşimlerin kaynama noktasını nasıl etkilediğine bir göz atalım. Birçok moleküller arası etkileşim, dipol adı verilen eşit olmayan elektron yoğunluğuna sahip alanları içerir. Tüm moleküllerin elektron dağılımlarında kısa dalgalanmalar vardır, bu nedenle polar olmayan moleküller bile geçici olarak dipollere sahip olabilir. Buna karşılık, yakındaki moleküllerde karşıt dipoller oluşur.
Geçici ve indüklenmiş dipoller arasındaki çekici kuvvetlere London dispersiyon kuvvetleri denir ve bunlar hidrokarbonlar gibi polar olmayan moleküller arasındaki baskın etkileşimlerdir. London dağılım kuvvetleri, çok elektronlu büyük moleküller arasında daha güçlüdür, çünkü bu moleküller elektronlarını zayıf tutar ve komşu moleküllerin elektron dağılımlarını etkilemesini kolaylaştırır.
Örneğin, yüksek moleküler ağırlıklı dallanmamış bir alkan, daha düşük moleküler ağırlıklı dallanmamış bir alkandan daha yüksek bir kaynama noktasına sahiptir. Ek olarak, dallanmamış bir alkan, daha yüksek yüzey alanı nedeniyle karşılaştırılabilir bir moleküler ağırlığa sahip dallı bir alkandan daha yüksek bir kaynama noktasına sahiptir.
Polar bağlara sahip moleküllerin kalıcı dipolleri vardır, bu da aralarında düzenli dipol-dipol etkileşimlerini sağlar. Dipol-dipol etkileşimleri London dispersiyon kuvvetlerinden daha güçlüdür, bu nedenle polar sıvıları kaynatmak genellikle polar olmayan sıvılardan daha fazla termal enerji gerektirir. Örneğin, polar bir molekül olan bir kloropentanın kaynama noktası 108 °C'dir. Yüzey alanı benzer olan ancak dipol içermeyen heksan, daha düşük bir kaynama noktasına sahiptir.
Hem daha elektronegatif bir atoma kovalent olarak bağlı bir hidrojene sahip moleküller hem de yalnız bir çift elektrona sahip elektron çeken bir atom hidrojen bağı yapabilir. Hidrojen bağları, dipol-dipol etkileşimlerinden ve London dağılım kuvvetlerinden daha güçlüdür, bu nedenle bunların üstesinden gelmek için daha da fazla termal enerji gerekir. Örneğin, propan ve etanol benzer moleküler ağırlıklara ve yüzey alanlarına sahiptir. Ancak propanın kaynama noktası etanolünkinden çok daha düşüktür çünkü etanol molekülleri birbirleriyle hidrojen bağları oluşturabilirken propan oluşturamaz.
Bu laboratuvarda, iki organik çözücünün kaynama noktasını belirlemek için kılcal damar yöntemini kullanacaksınız.

kaynama noktaları

Kaynama Noktası Tayini
Erime noktasına benzer şekilde, kaynama noktası da fiziksel bir özelliktir. Numune saf bir bileşikse, bileşiğin kimliğini belirlemek için kaynama noktası kullanılabilir. Sonuç olarak, deneysel olarak tam kaynama noktasını belirlemek zordur. Erime noktaları gibi, deneysel kaynama noktaları da bir aralık olarak verilir ve gerçek literatür değerinden birkaç derece değişir.
Buhar Basıncı
Çözeltinin tanıdık köpürmesi ile karakterize edilen bir çözücünün neden kaynadığını anlamak için, sıvı ve gaz fazları arasındaki dinamikleri anlamak önemlidir. Kapalı bir kapta saf bir sıvı bileşik düşünün. Sıvının yüzeyindeki moleküllerin bir kısmı, moleküller arası kuvvetlerin üstesinden gelmek ve gaz fazına girmek için yeterli enerjiye sahip olacaktır. Bununla birlikte, gaz fazındaki moleküller de enerji kaybedebilir ve tekrar yoğunlaşarak bir sıvıya dönüşebilir. Bu nedenle, bu sistemde rekabet eden iki süreç vardır: buharlaşma ve yoğunlaşma.
Buharlaşma hızı yoğuşma hızına eşit olduğunda, sistem bir denge durumuna ulaşmıştır. Bu, gaz fazına giren her molekül için bir diğerinin sıvı faza yoğunlaştığı ve kap içindeki sıvı veya gaz miktarında net bir kazanç veya kayıp olmadığı anlamına gelir. Denge kurulduktan sonra, buharın sıvının üzerine uyguladığı basınca buhar basıncı denir. Bir sıvının buharlaşma eğilimine uçuculuğu denir. Daha uçucu bir sıvı daha yüksek bir buhar basıncına sahipken, daha az uçucu bir sıvı daha düşük bir buhar basıncına sahiptir.
Buhar basıncı sıcaklığa göre değişir. Çözeltinin sıcaklığını arttırırsanız, daha fazla molekül sıvı fazdan kaçmak için yeterli enerjiye sahip olur ve böylece buhar basıncı artar. Sonuçta, yeterli ısı uygulanırsa, sıvı ve gaz arasındaki arayüzde olmayan moleküller gaz fazına geçecek ve kaynama ile ilişkilendirdiğimiz tanıdık kabarcıkları oluşturacaktır.
Bir sıvının kaynama noktasına, sıvının toplam buhar basıncı atmosfer basıncına eşit olduğunda ulaşılır. Bunun meydana geldiği sıcaklığa kaynama noktası denir. Daha yüksek rakımlarda ve dolayısıyla daha düşük bir atmosfer basıncında, buhar basıncını atmosfer basıncına yükseltmek için daha az ısı gerektiğinden, bir sıvı daha düşük bir sıcaklıkta kaynar. Ek olarak, uçuculuk veya bir çözücünün buharlaşma yeteneği de buhar basıncını etkiler. Yüksek uçuculuğa sahip çözücüler, daha düşük uçuculuğa sahip çözücülerden daha yüksek buhar basıncına sahiptir.
Kaynama Noktasını Etkileyen Faktörler
Erime noktaları ile kaynama noktaları arasındaki benzerlik, bir bileşiğin erime noktasını etkileyen aynı faktörlerin kaynama noktasını da etkileyeceği anlamına gelir. Bu nedenle, sıvı bileşik içinde bulunan moleküller arası kuvvetlerin gücü ve türleri kaynama noktasını etkileyecektir. Üç tür moleküler kuvvet olduğunu hatırlayın: hidrojen bağı, dipol-dipol etkileşimleri ve Londra Dispersiyon kuvvetleri. Bunların her birinin farklı çekim güçleri vardır ve üstesinden gelmek için farklı miktarlarda enerji gerektirir. Hidrojen bağı yapabilen bileşikler, yalnızca London dispersiyon kuvvetleri ile etkileşime girebilen bileşiklerden daha yüksek kaynama noktalarına sahip olacaktır. Kaynama noktaları için ek bir husus, bileşiğin buhar basıncını ve uçuculuğunu içerir. Tipik olarak, bir bileşik ne kadar uçucu olursa, kaynama noktası o kadar düşük olur.
Kaynama noktasını belirlemek için kılcal yöntem
Bir organik bileşiğin kaynama noktasını belirlemek için basit bir yöntem, kılcal yöntemi kullanmaktır. Bu kurulumda, boş bir cam kılcal boru, sıvı fazda saf bileşiğin bir kabına ters çevrilir. Sıvı ısıtıldıkça, numunenin buhar basıncı artar ve gaz halindeki buhar cam kılcal boruya girmeye başlar. Bu, içeride sıkışan havayı dışarı atar ve kılcal borunun altından çıkan kabarcıklara neden olur. Bu noktada sıvının soğumasına izin verilir. Numunenin buhar basıncı, cam kılcal borunun içindeki atmosferik basınçla aynı olduğunda, sıvı tüpe girmeye başlayacaktır. Bu fenomen meydana geldiğinde çözeltinin sıcaklığı, sıvı bileşiğin kaynama noktasıdır.

Kaynama noktaları

Kaynama Noktası Tayini
Erime noktasına benzer şekilde, kaynama noktası da fiziksel bir özelliktir. Numune saf bir bileşikse, kaynatma ...

Education

JoVE Lab Manual

Chemistry

Kimya

boiling point and vapor pressure

Boiling point and vapor pressure are key physical properties of a liquid. For a pure compound, the boiling point can help identify the substance. In experiments, the boiling point is usually recorded as a range because exact values are hard to measure and may differ by a few degrees from the literature value.

Vapor pressure explains why a liquid boils. In a sealed container, some molecules at the liquid surface gain enough energy to escape into the gas phase. At the same time, some gas molecules lose energy and condense back into the liquid. When evaporation and condensation happen at the same rate, the system is at equilibrium. The pressure from the vapor above the liquid is the vapor pressure.

Volatility is the tendency of a liquid to vaporize. A more volatile liquid has a higher vapor pressure, while a less volatile liquid has a lower vapor pressure. Vapor pressure also changes with temperature. As temperature rises, more molecules can escape the liquid, so vapor pressure increases. With enough heat, molecules inside the liquid also change to gas and form the bubbles seen during boiling.

A liquid boils when its total vapor pressure matches atmospheric pressure. That temperature is the boiling point. Because atmospheric pressure changes with elevation, a liquid boils at a lower temperature at higher elevations. Less atmospheric pressure means less heat is needed for the vapor pressure to reach that level.

Intermolecular forces also affect boiling point. These forces include hydrogen bonding, dipole-dipole interactions, and London dispersion forces. They differ in strength, so different amounts of energy are needed to overcome them. Compounds that can hydrogen bond usually have higher boiling points than compounds that rely only on London dispersion forces. Volatility matters too. In general, more volatile compounds have lower boiling points.

One simple way to measure a boiling point is the capillary method. An empty glass capillary tube is placed upside down in the liquid sample. As the sample is heated, its vapor pressure rises and vapor enters the tube. This pushes out trapped air and causes bubbles to appear from the bottom of the capillary tube. The sample is then allowed to cool. When liquid begins to rise into the tube, the vapor pressure inside the tube matches the atmospheric pressure. The temperature at that moment is the boiling point of the compound.

Boiling Point and Vapor Pressure

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Reaction Order and Rate Constants

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Reaction Rate, Arrhenius, and Catalysts

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electrolytic cells

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melting points

How Impurities Change Melting Points

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boiling points

Boiling point and vapor pressure are key physical properties of a liquid. For a pure compound, the boiling point can help identify the substance. In experiments, the boiling point is usually recorded as a range because exact values are hard to measure and may differ by a few degrees from the literature value. Vapor pressure explains why a liquid boils. In a sealed container, some molecules at the liquid surface gain enough energy to escape into the gas phase. At the same time, some gas...

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Purifying Crystals by Solubility

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extraction

Separating Mixtures with Solvent Extraction

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simple distillation

Separating Liquids by Boiling Point

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steam distillation

Steam Distillation and Low-Boiling Separation

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TLC Separation by Polarity

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column chromatography

Separating Mixtures by Polarity

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identification-of-unknown-aldehydes-and-ketones

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How Dyes Absorb Visible Light

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chemistry

Kimya laboratuvar temelleri için, hem eğitmenlere hem de öğrencilere yönelik, kapsamlı ve müfredat odaklı vidolar.

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Explore how vapor pressure, volatility, and intermolecular forces affect boiling point, and learn how the capillary method measures it in the lab.

Boiling Point and Vapor Pressure | JoVE K12

Kaynama noktaları öğretimine bu 1 dakikalık eğitmen rehberiyle hazırlanın. JoVE Lab Manual üzerindeki Chemistry laboratuvarı için temel hazırlık adımlarını kapsar.

Chemistry içinde Kaynama noktaları Eğitmen Hazırlığı - 4.9K+ Görüntülenme | JoVE Lab Manual

6 dakikalık bu öğrenci protokol videosunda Kaynama noktaları prosedürlerini adım adım takip edin. JoVE Lab Manual üzerindeki Chemistry koleksiyonunun bir parçasıdır.

Chemistry içinde Kaynama noktaları Öğrenci Protokolü - 90K+ Görüntülenme | JoVE Lab Manual

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Boiling Point and Vapor Pressure

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