Name: temperature effects on gibbs free energy
Uploaded: 2023-04-30T18:28:32.000Z
Duration: 2 min 23 s
Channel: JoVE

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gibbs-free-energy-and-thermodynamic-favorability

Gibbs Free Energy and Thermodynamic Favorability

التغيير في طاقة جيبس الحرة ، أو دلتا جي ، هو الطاقة التي يتم امتصاصها أو إطلاقها عند تكوين روابط تخزين الطاقة أو كسرها ، على التوالي.
تعتمد علامة دلتا G على العلامات والقيم النسبية للمحتوى الحراري والإنتروبيا ودرجة الحرارة.
إذا كانت دلتا H سالبة ودلتا S موجبة ، فإن دلتا G سالبة في جميع درجات الحرارة. وبالتالي ، فإن التفاعلات الطاردة للحرارة حيث تزداد إنتروبيا النظام تكون دائما عفوية.
إذا كانت كل من دلتا H ودلتا S سالبة ، فإن دلتا G تعتمد على درجة الحرارة. تكون التفاعلات ذات المحتوى الحراري السلبي والتغيرات الانتروبية عفوية فقط في درجات الحرارة المنخفضة.
تعتمد دلتا G أيضا على درجة الحرارة إذا كانت كل من دلتا H ودلتا S موجبة. تكون التفاعلات ذات المحتوى الحراري الإيجابي والتغيرات الانتروبية عفوية فقط في درجات الحرارة المرتفعة.
عندما تكون دلتا H موجبة ودلتا S سالبة ، تكون دلتا G موجبة دائما ، ويكون التفاعل غير عفوي في جميع درجات الحرارة.
بالنسبة لأي تركيبة خليط تفاعل ، فإن دلتا G للتفاعل هي مجموع الطاقة الحرة القياسية و RT مضروبا في السجل الطبيعي لحاصل التفاعل.
عندما تكون المواد المتفاعلة والمنتجات في حالة توازن، يكون تغير الطاقة الحرة صفرا، وحاصل التفاعل يساوي ثابت التوازن. لذلك ، فإن تغيير الطاقة الحرة القياسي يساوي سالب RT ln (K).
إذا كانت دلتا G صفر أقل من صفر ، فإن ln (K) موجبة ، مما يعني أن K أكبر من 1. في هذه الحالة ، يفضل تكوين المنتج عند التوازن. كلما زاد ثابت التوازن ، زاد الانخفاض في طاقة جيبس الحرة. 
تتضمن التفاعلات ذات القيم السلبية دلتا G إطلاق طاقة حرة إلى المناطق المحيطة وتسمى التفاعلات "الطاردة للطاقة".
على العكس من ذلك ، إذا كانت دلتا G صفر أكبر من صفر ، فإن ln (K) سالبة ، مما يعني أن K أقل من 1 ، ويفضل الاتجاه العكسي للتفاعل.
تمتص التفاعلات ذات دلتا G الموجبة الطاقة الحرة من المناطق المحيطة وتسمى التفاعلات "endergonic".

الطاقة الحرة لجيبس والأفضلية الديناميكية الحرارية

<div style="direction:rtl">تعتمد تلقائية العملية على درجة حرارة النظام. على سبيل المثال، ستتم التحولات الطورية تلقائيًا في اتجاه أو آخر اعتمادًا على درجة حرارة المادة المعنية. وبالمثل، يمكن لبعض التفاعلات الكيميائية أيضًا أن تظهر تلقائية تعتمد على درجة الحرارة. لتوضيح هذا المفهوم، يتم النظر في المعادلة التي تربط التغير في الطاقة الحرة بالتغيرات في المحتوى الحراري والانتروبيا للعملية:
<img alt="Eq1" src="/files/ftp_upload/11694/11694%20PT%20eq%201.svg" style="text-align: center; height: 15px;">
يتم بعد ذلك تحديد تلقائية العملية، كما يتضح في العلامة الحسابية لتغير طاقتها الحرة، من خلال علامات تغيرات المحتوى الحراري والإنتروبيا، وفي بعض الحالات، درجة الحرارة المطلقة. بما أن T هي درجة الحرارة المطلقة (كلفن)، فيمكن أن تكون لها قيم موجبة فقط. وبالتالي توجد أربعة احتمالات فيما يتعلق بعلامات تغيرات الإنثالبي والإنتروبيا:

<ol>
	<li style="text-align: right;">كل من ΔH وΔS إيجابيان. تصف هذه الحالة عملية ماصة للحرارة تتضمن زيادة في إنتروبيا النظام. في هذه الحالة، ستكون قيمة ΔG سالبة إذا كان حجم الحد TΔS أكبر من ΔH. إذا كان الحد TΔS أقل من ΔH، فسيكون تغير الطاقة الحرة موجبًا. تكون مثل هذه العملية تلقائية عند درجات الحرارة المرتفعة وغير عفوية عند درجات الحرارة المنخفضة.</li>
	<li style="text-align: right;">كلا من ΔH وΔS سلبيان. تصف هذه الحالة عملية طاردة للحرارة تتضمن انخفاضًا في إنتروبيا النظام. في هذه الحالة، ستكون قيمة ΔG سالبة إذا كان حجم الحد TΔS أقل من ΔH. إذا كان حجم الحد TΔS أكبر من ΔH، فسيكون تغير الطاقة الحرة موجبًا. تكون هذه العملية تلقائية عند درجات الحرارة المنخفضة وغير عفوية عند درجات الحرارة المرتفعة.</li>
	<li style="text-align: right;">ΔH موجبة وΔS سالبة. تصف هذه الحالة عملية ماصة للحرارة تتضمن انخفاضًا في إنتروبيا النظام. في هذه الحالة، ستكون قيمة ΔG موجبة بغض النظر عن درجة الحرارة. تعتبر هذه العملية غير عفوية في جميع درجات الحرارة.</li>
	<li style="text-align: right;">ΔH سالبة وΔS موجبة. تصف هذه الحالة عملية طاردة للحرارة تتضمن زيادة في إنتروبيا النظام. في هذه الحالة، ستكون قيمة ΔG سالبة بغض النظر عن درجة الحرارة. تعتبر هذه العملية تلقائية في جميع درجات الحرارة.</li>
</ol>

يمكن النظر إلى تغير الطاقة الحر لعملية ما على أنه مقياس لقوتها الدافعة. تمثل القيمة السالبة لـ ΔG قوة دافعة للعملية في الاتجاه الأمامي، بينما تمثل القيمة الموجبة قوة دافعة للعملية في الاتجاه العكسي. عندما تكون ΔGrxn صفرًا، تكون القوى الدافعة للأمام والخلف متساوية، وتحدث العملية في كلا الاتجاهين بنفس المعدل (يكون النظام في حالة توازن).

تذكر أن Q هي القيمة العددية لتعبير الفعل الكتلي للنظام، ويمكن استخدام قيمتها لتحديد الاتجاه الذي سيستمر فيه التفاعل من أجل تحقيق التوازن. عندما تكون Q أقل من ثابت التوازن K، سيستمر التفاعل في الاتجاه الأمامي حتى يتم الوصول إلى التوازن و Q = K. وعلى العكس من ذلك، إذا كانت Q &gt; K، ستستمر العملية في الاتجاه المعاكس حتى يتم تحقيق التوازن.
يرتبط تغير الطاقة الحرة لعملية تحدث مع المواد المتفاعلة والمنتجات الموجودة تحت ظروف غير قياسية (ضغوط تزيد عن 100 كيلو باسكال؛ وتركيزات أخرى غير 1 مولار) بتغير الطاقة الحرة القياسية وفقًا لهذه المعادلة:

<img alt="Eq2" src="/files/ftp_upload/11694/11694%20PT%20eq%202.svg" style="text-align: center; height: 18px;">

R هو ثابت الغاز (8.314 J/K mol)، T هو الكلفن أو درجة الحرارة المطلقة، وQ هو حاصل التفاعل. بالنسبة لنظام في حالة توازن، Q = K و ΔG = 0، ويمكن كتابة المعادلة السابقة بالشكل

<img alt="Eq3" src="/files/ftp_upload/11694/11694%20PT%20eq%203.svg" style="text-align: center; height: 18px;">
<img alt="Eq4" src="/files/ftp_upload/11694/11694%20PT%20eq%204.svg" style="text-align: center; height: 18px;">

يوفر هذا النموذج من المعادلة رابطًا مفيدًا بين هاتين الخاصيتين الديناميكيتين الحراريتين الأساسيتين، ويمكن استخدامه لاشتقاق ثوابت التوازن من تغيرات الطاقة الحرة القياسية والعكس. تم تلخيص العلاقات بين تغيرات الطاقة الحرة القياسية وثوابت التوازن أدناه.

إذا كانت K &gt; 1، ΔG° &lt; 0 وكانت المنتجات أكثر وفرة في خليط التفاعل.
إذا كانت K &lt; 1، ΔG° &gt; 0 وكانت المواد المتفاعلة أكثر وفرة في خليط التفاعل.
إذا كانت K = 1، ΔG° = 0 وكانت المواد المتفاعلة والمنتجات وفيرة نسبيًا في خليط التفاعل.

هذا النص مقتبس من <a href="https://openstax.org/books/chemistry-2e/pages/16-4-free-energy">Openstax, Chemistry 2e, Section 16.4: Free Energy.</a>  

</div>

تعتمد عفوية العملية على درجة حرارة النظام. انتقالات الطور ، على سبيل المثال ، ستستمر تلقائيا في اتجاه واحد أو ...

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temperature effects on gibbs free energy

Temperature changes can decide whether a process is spontaneous. This idea applies to phase changes and to some chemical reactions. The key link is Gibbs free energy, which connects free energy change with enthalpy and entropy.

The sign of the Gibbs free energy change, or ΔG, depends on the signs of enthalpy change (ΔH) and entropy change (ΔS), and sometimes on the absolute temperature. Because temperature is measured in kelvin, it is always a positive value. That means there are four main sign combinations to consider.

If both ΔH and ΔS are positive, the process is endothermic and the system gains entropy. In this case, ΔG is negative only when the TΔS term is larger than ΔH. So the process is spontaneous at high temperatures and nonspontaneous at low temperatures. If both ΔH and ΔS are negative, the process is exothermic and the system loses entropy. Then ΔG is negative when the TΔS term is smaller than ΔH, which makes the process spontaneous at low temperatures and nonspontaneous at high temperatures.

If ΔH is positive and ΔS is negative, the process is endothermic and the system becomes less disordered. In that case, ΔG stays positive at any temperature, so the process is nonspontaneous at all temperatures. If ΔH is negative and ΔS is positive, the process is exothermic and the system becomes more disordered. Then ΔG stays negative at any temperature, so the process is spontaneous at all temperatures.

Gibbs free energy also shows the driving force of a process. A negative ΔG means the forward direction is favored. A positive ΔG means the reverse direction is favored. When ΔGrxn is zero, the forward and reverse driving forces are equal, and the system is at equilibrium.

The reaction quotient, Q, helps predict which way a reaction will shift to reach equilibrium. When Q is less than the equilibrium constant, K, the reaction moves forward until Q = K. When Q is greater than K, the process moves in reverse until equilibrium is reached. Under nonstandard conditions, the free energy change is related to the standard free energy change by ΔG = ΔG° + RT ln Q, where R is the gas constant and T is the kelvin temperature.

At equilibrium, Q equals K and ΔG is zero, so the equation can be written as a link between ΔG° and K. This relationship lets chemists find equilibrium constants from standard free energy changes, or the reverse. If K is greater than 1, ΔG° is negative and products are more abundant. If K is less than 1, ΔG° is positive and reactants are more abundant. If K equals 1, ΔG° is zero and reactants and products are present in similar amounts.

Temperature Effects on Gibbs Free Energy

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bond dissociation energy and activation energy

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Electric Dipoles and Dipole Moment

Consider two charges of equal magnitude but opposite signs. If they cannot be separated by an external electric field, the system is called a permanent ...

Plan and conduct an investigation to gather evidence to compare the structure of substances at the macroscale to infer the strength of electrical forces between particles.  Clarification Statement: Emphasis is on understanding the strengths of forces between particles, not on naming specific intermolecular forces (such as dipole-dipole). Examples of particles could include ions, atoms, molecules, and network solids (such as graphite). Examples of macro-properties of substances could include the melting point and boiling point, vapor pressure, and surface tension.

HS-PS1-3

Bond Dissociation Energy and Activation Energy

Bond energy is the energy required to break a bond homolytically. These values are usually expressed in units of kcal/mol or kJ/mol and are referred to as ...

Bond Energies and Bond Lengths

Stable molecules exist because covalent bonds hold the atoms together. The strength of a covalent bond is measured by the energy required to break it, ...

Coupled Reactions

Cellular processes such as building and breaking down complex molecules occur through stepwise chemical reactions. Some of these chemical reactions are ...

Energy Diagrams, Transition States, and Intermediates

Free-energy diagrams, or reaction coordinate diagrams, are graphs showing the energy changes that occur during a chemical reaction. The reaction ...

What is Metabolism?

Overview

Metabolism represents all of the chemical activity in a cell, including reactions that build molecules (anabolism) and those that break ...

types-of-chemical-reactions-anabolic-and-catabolic

Types of Chemical Reactions: Anabolic and Catabolic

The first law of thermodynamics holds that energy can neither be created nor destroyed&#8212;it can only change form. An organism&#39;s essential function ...

Non-equilibrium in the Cell

An important concept in studying metabolism and energy is that of chemical equilibrium. Most chemical reactions are reversible. They can proceed in both ...

Activation Energy

Activation energy is the minimum amount of energy necessary for a chemical reaction to move forward. The higher the activation energy, the slower the rate ...

Energy Transfer in Chemical Reactions

Chemical reactions require sufficient energy to cause the matter to collide with enough precision and force that old chemical bonds can be broken and new ...

factors-influencing-the-rate-of-chemical-reactions

Factors Influencing the Rate of Chemical Reactions

A variety of factors influence the rate of chemical reactions. For a chemical reaction to happen, atoms must collide with enough energy to overcome the ...

Predicting Reaction Outcomes

Kinetics describes the rate and path by which a reaction occurs. In contrast, thermodynamics deals with state functions and describes the properties, ...

States of Matter and Phase Changes

The internal energy of a substance&#8212;the total kinetic energy of all its molecules and the potential energy of their associated forces&#8212;depends ...

Reaction Mechanisms

Chemical reactions often occur in a stepwise fashion, involving two or more distinct reactions taking place in a sequence. A balanced equation indicates ...

Temperature Dependence

Chemical Kinetics 
The reaction rate is the speed at which a chemical reaction occurs. The reaction rate is defined as the change in concentration of a ...

Molecular Kinetic Energy

The word &#34;gas&#34;&#160;comes from the Flemish word meaning &#34;chaos,&#34; first used to describe vapors by the chemist J. B. van Helmont. Consider ...

Energy Basics

Chemical reactions, such as those that occur when you light a match, involve changes in energy as well as matter.

Chemical changes and their accompanying ...

Reaction Rate

The rate of reaction is the change in the amount of a reactant or product per unit time. Reaction rates are therefore determined by measuring the time ...

Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.  Clarification Statement: Emphasis is on the idea that a chemical reaction is a system that affects the energy change.  Examples of models could include molecular-level drawings and diagrams of reactions, graphs showing the relative energies of reactants and products, and representations showing energy is conserved.

HS-PS1-4

Temperature Effects on Gibbs Free Energy

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