Name: heat changes in chemical equations
Uploaded: 2020-09-03T13:38:27.000Z
Duration: 2 min 55 s
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

Thermochemical Equations

Kimyasal reaksiyonların çoğu atmosferik basınçta gerçekleşir. Sabit basınç koşulları altında, reaksiyonla ilişkili ısı değişimi delta Q, entalpi delta H'deki değişime eşittir, aynı zamanda reaksiyon ısısı veya entalpi olarak da adlandırılır. Reaksiyon entalpisi, ürünlerin ve reaktanların entalpileri arasındaki farktır.Ürünlerin entalpisi reaktanların entalpisinden büyük olduğunda delta H pozitiftir. Bu tür reaksiyonlar çevreden ısı alır ve endotermiktir. Aksine, reaktanların entalpisi ürünlerin entalpisinden büyükse delta H negatiftir.Bu tür reaksiyonlar ısı açığa çıkarır ve ekzotermiktir. Herhangi bir kimyasal reaksiyon için, eşlik eden entalpi değişiminin büyüklüğü, dengelenmiş denklemin katsayıları ile gösterildiği gibi, reaktanların ve ürünlerin stokiyometrik miktarlarına bağlıdır. Faz etiketlerini ve reaksiyon entalpisini içeren dengeli bir kimyasal denklem olan delta H, termokimyasal denklem olarak adlandırılır.Birincil yakıt kaynağımız olan metanın yanmasını düşünelim. Yanan metan çevreye ısı yayar. Reaksiyonun ekzotermik doğası, termokimyasal denklemdeki negatif entalpi değişimi ile gösterilir.Yanma denklemi, bir mol metan gazı 2 mol oksijen gazı ile reaksiyona girerek 1 mol karbondioksit gazı ve 2 mol sıvı su verdiğinde çevreye 890, 8 kilojoule ısı salındığını göstermektedir. Reaktanlar veya ürünler arasındaki molar oran ve reaksiyon ısısı, reaksiyon sırasında alışverişi yapılan ısıyı hesaplamak için dönüşüm faktörleri olarak kullanılabilir. Bir gaz silindiri 25, 5 kilogram metan içeriyorsa ve silindirdeki metanın tamamı yanmaya uğrarsa, ne kadar ısı üretilir?Genel olarak kavramsal tutum, kütleyi mollere ve ardından molleri reaksiyon ısısına dönüştürmektir. Başlangıç olarak, kütleyi gram olarak bulmak için 25, 5 kilogram 1000 ile çarpılır. Daha sonra, metan kütlesi 1594 mol metan verecek şekilde molar kütlesine bölünür mol başına 16, 0 gram.Son olarak, metan molleri ile reaksiyon ısısı arasındaki dönüşüm faktörünü kullanarak, 1594 mol metan, 14, 2 çarpı 10 üzeri 6 kilojul ısı açığa çıkarır ve bu ısı reaksiyonun ısısıdır. Sonuç negatiftir çünkü reaksiyonda ısı üretildiği için süreç ekzotermiktir.

<ol>
	<li>Canagaratna, Sebastian G. "Entalpi hesaplamalarında görsel bir yardım." Kimya Eğitimi Dergisi 77, no. 9 (2000): 1178.</li>
	<li>Keifer, David. "Entalpi ve Termodinamiğin İkinci Yasası." Kimya Eğitimi Dergisi 96, no. 7 (2019): 1407-1411.</li>
	<li>Halil, Mutasım I. "Matris yöntemi ile reaksiyon entalpisinin hesaplanması." Kimya Eğitimi Dergisi 77, no. 2 (2000): 185. 
	 </li>
</ol>

termokimyasal denklemler

Sabit basınçta gerçekleştirilen bir kimyasal reaksiyon (sistem) için - genleşme veya daralmanın neden olduğu tek işle - reaksiyon entalpisi (aynı zamanda reaksiyon ısısı, ΔHrxn) olarak da adlandırılır), çevre ile değiştirilen ısıya eşittir (qp).
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/799/799_Equations-01.png" style="height: 40px;" />
 
 Entalpideki değişiklik kapsamlı bir özelliktir ve reaksiyona katılan reaktanların miktarına (veya reaktanların mol sayısına) bağlıdır. Entalpideki değişim reaksiyona özeldir ve reaktan ve ürün türlerinin fiziksel durumları önemlidir. Bir ekzotermik reaksiyon, −ΔHrxn değeriyle karakterize edilirken, bir endotermik reaksiyon, +ΔHrxn değerine sahiptir. 
 
 Bir reaksiyon tarafından açığa çıkan veya absorblanan ısı miktarı, reaksiyon tarafından tüketilen veya üretilen her bir maddenin miktarına karşılık geldiğinden, hem madde hem de enerjideki değişiklikleri temsil etmek için termokimyasal denklem kullanmak uygundur. Termokimyasal bir denklemde, bir reaksiyonun entalpisindeki değişim ΔHrxn olarak gösterilir ve genellikle reaksiyon denklemi takip edilerek sağlanır. ΔHrxn'nin büyüklüğü, kimyasal denklemde gösterilen reaksiyonla ilişkili ısı miktarını gösterir. ΔHrxn işareti, reaksiyonun ekzotermik mi yoksa endotermik mi olduğunu gösterir. Aşağıdaki denklemde, 1 mol hidrojen gazı ve 1/2 mol oksijen gazı (bir miktar sıcaklık ve basınçta) 1 mol sıvı su (aynı sıcaklık ve basınçta) oluşturmak üzere reaksiyona girer.
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/799/799_Equations-02.png" style="height: 40px;" />
 
 Bu denklem çevreye 286 kJ ısı salındığını gösterir. Başka bir deyişle, tüketilen her mol hidrojen veya üretilen her mol su için 286 kJ ısı açığa çıkar (reaksiyon ekzotermiktir). Bu nedenle, reaksiyon entalpisi, belirli miktarlarda reaktan ve ürünleri içeren reaksiyonlar sırasında açığa çıkan veya absorblanan ısı miktarını hesaplamak için kullanılabilen bir dönüştürme faktörüdür.
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/799/799_Equations-03.png" style="height: 80px;" />
 
 Kimyasal denklemin katsayıları bir faktörle çarpılırsa (yani, bir maddenin miktarı değiştirilirse), entalpi değişiminin aynı faktörle çarpılması gerekir.
 
 (miktarlarda iki kat artış)
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/799/799_Equations-04.png" style="height: 40px;" />
 
 (miktarlarda iki kat azalma)
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/799/799_Equations-05.png" style="height: 40px;" />
 
 Bir reaksiyonun entalpi değişiminin reaktanların ve ürünlerin fiziksel durumlarına bağlı olduğunu göstermek için, gaz halindeki su (veya su buharı) oluşumunu düşünün. 1 mol hidrojen gazı ve ½ mol oksijen gazı reaksiyona girerek 1 mol gaz halinde su oluşturduğunda, sıvı su oluştuğunda açığa çıkan 286 kJ ısının aksine sadece 242 kJ ısı açığa çıkar.
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/799/799_Equations-06.png" style="height: 40px;" />

Termokimyasal Denklemler

Sabit basınçta gerçekleştirilen bir kimyasal reaksiyon (sistem) için - genleşme veya büzülmeden kaynaklanan tek iş ile - ...

Education

JoVE Core

Kimya

Thermochemistry

Termokimya

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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 positive one. For that reason, a thermochemical equation is useful because it shows both the chemical change and the energy change together.

In a thermochemical equation, ΔHrxn is written after the chemical equation. Its magnitude tells how much heat is linked to the reaction as written. Its sign shows whether the reaction is exothermic or endothermic in that form.

For example, 1 mole of hydrogen gas and 1/2 mole of oxygen gas can react to form 1 mole of liquid water. This reaction releases 286 kJ of heat to the surroundings. That means 286 kJ is released for every mole of hydrogen used or every mole of water made, so ΔHrxn can act like a conversion factor.

If the coefficients in the chemical equation are multiplied, the enthalpy change must be multiplied by the same factor. A two-fold increase in the amounts gives a two-fold increase in ΔHrxn, and a two-fold decrease gives a two-fold decrease. The physical state matters too. When the same reaction makes gaseous water instead of liquid water, only 242 kJ of heat are released.

Heat Changes in Chemical Equations

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, 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...

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 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

Learn how ΔHrxn shows heat released or absorbed in reactions, why equation coefficients matter, and how physical state changes the enthalpy value.

Heat Changes in Chemical Equations | 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

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.8

IPC.8.B

Pennsylvania State Academic Standards

Physical Science

Chemical Reactions

3.2.9-12.D

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Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Tennessee Academic Standards

CHEM1.PS3.3

Virginia  Standards of Learning

HIgh School

CH.7

CH.7.a

CH.7.c

CHEM.13

CHEM.13.A

CHEM.13.C

Florida Department of Education

SC.912.P.10

SC.912.P.10.7

Georgia Standards of Excellence

SC3.

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PS.Chm.7.1

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Enthalpy

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

Heat Changes in Chemical Equations

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