Name: temperature effects on gibbs free energy
Uploaded: 2023-04-30T18:28:32.000Z
Duration: 2 min 23 s
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Gibbs Free Energy and Thermodynamic Favorability

השינוי באנרגיה החופשית של גיבס, או דלתא G, הוא האנרגיה הנספגת או משתחררת כאשר קשרים אוגרי אנרגיה נוצרים או נשברים, בהתאמה.
הסימן של דלתא G תלוי בסימנים ובערכים היחסיים של אנתלפיה, אנטרופיה וטמפרטורה.
אם דלתא H שלילית ודלתא S חיובית, דלתא G שלילית בכל הטמפרטורות. לכן, תגובות אקסותרמיות שבהן האנטרופיה של המערכת גדלה הן תמיד ספונטניות.
אם גם דלתא H וגם דלתא S שליליות, דלתא G תלויה בטמפרטורה. תגובות עם שינויים שליליים באנתלפיה ובאנטרופיה הן ספונטניות רק בטמפרטורות נמוכות.
דלתא G תלויה גם בטמפרטורה אם גם דלתא H וגם דלתא S חיוביות. תגובות עם שינויים חיוביים באנתלפיה ובאנטרופיה הן ספונטניות רק בטמפרטורות גבוהות יותר.
כאשר דלתא H חיובית ודלתא S שלילית, דלתא G תמיד חיובית, והתגובה אינה ספונטנית בכל הטמפרטורות.
עבור כל הרכב תערובת תגובה, הדלתא G עבור התגובה היא סכום האנרגיה החופשית הסטנדרטית ו-RT כפול היומן הטבעי של מנת התגובה.
כאשר המגיבים והתוצרים נמצאים בשיווי משקל, שינוי האנרגיה החופשית הוא אפס, ומנת התגובה שווה לקבוע שיווי המשקל. לכן, שינוי האנרגיה החופשית הסטנדרטי שווה ל- RT ln(K) שלילי.
אם דלתא G naught קטן מאפס, ln(K) הוא חיובי, כלומר K גדול מ-1. במקרה זה, היווצרות המוצר מועדפת בשיווי משקל. ככל שקבוע שיווי המשקל גדול יותר, כך גדלה הירידה באנרגיה החופשית של גיבס. 
תגובות עם ערכי דלתא G שליליים כרוכות בשחרור אנרגיה חופשית לסביבה ונקראות תגובות "אקסרגוניות".
לעומת זאת, אם דלתא G naught גדול מאפס, ln(K) הוא שלילי, כלומר K קטן מ-1, והכיוון ההפוך של התגובה מועדף.
תגובות עם דלתא G חיובית סופגות אנרגיה חופשית מהסביבה ונקראות תגובות "אנדרגוניות".

﻿אנרגיה חופשית של גיבס והעדפה תרמודינמית

<div style="direction:rtl"> הספונטניות של תהליך תלויה בטמפרטורה של המערכת. מעברי מצב צבירה, למשל, יתנהלו באופן ספונטני בכיוון זה או אחר בהתאם לטמפרטורה של החומר המדובר. כמו כן, תגובות כימיות מסוימות יכולות גם להפגין ספונטניות תלויות טמפרטורה. כדי להמחיש מושג זה, המשוואה המתייחסת לשינוי אנרגיה חופשית לשינויי האנתלפיה והאנטרופיה עבור התהליך נחשבת: <img alt="Eq1" src="/files/ftp_upload/11694/11694%20PT%20eq%201.svg" style="text-align: center; height: 15px;"> הספונטניות של תהליך, כפי שהיא משתקפת בסימן האריתמטי של שינוי האנרגיה החופשית שלו, נקבעת אז על ידי סימני השינויים באנטלפיה והאנטרופיה, ובמקרים מסוימים, הטמפרטורה המוחלטת. מכיוון ש-T היא הטמפרטורה המוחלטת (קלווין), יכולים להיות לה רק ערכים חיוביים. קיימות אפוא ארבע אפשרויות ביחס לסימני השינויים באנטלפיה והאנטרופיה: 1 גם ΔH וגם ΔS חיוביים. מצב זה מתאר תהליך אנדותרמי הכולל עלייה באנטרופיית המערכת. במקרה זה, ΔG יהיה שלילי אם גודל המונח TΔS גדול מ- ΔH. אם מונח TΔS קטן מ- ΔH, שינוי האנרגיה החופשית יהיה חיובי. תהליך כזה הוא ספונטני בטמפרטורות גבוהות ולא ספונטני בטמפרטורות נמוכות. 2 גם ΔH וגם ΔS שליליים. מצב זה מתאר תהליך אקסותרמי הכולל ירידה באנטרופיית המערכת. במקרה זה, ΔG יהיה שלילי אם גודל האיבר TΔS קטן מ-ΔH. אם גודל המונח TΔS גדול מ- ΔH, שינוי האנרגיה החופשית יהיה חיובי. תהליך כזה הוא ספונטני בטמפרטורות נמוכות ולא ספונטני בטמפרטורות גבוהות. 3 ΔH חיובי ו-ΔS שלילי. מצב זה מתאר תהליך אנדותרמי הכולל ירידה באנטרופיית המערכת. במקרה זה, ΔG יהיה חיובי ללא קשר לטמפרטורה. תהליך כזה אינו ספונטני בכל הטמפרטורות. 4 ΔH שלילי ו-ΔS חיובי. מצב זה מתאר תהליך אקסותרמי הכולל עלייה באנטרופיית המערכת. במקרה זה, ΔG יהיה שלילי ללא קשר לטמפרטורה. תהליך כזה הוא ספונטני בכל הטמפרטורות. ניתן להתייחס לשינוי האנרגיה החופשית עבור תהליך כמדד לכוח המניע שלו. ערך שלילי עבור ΔG מייצג כוח מניע לתהליך בכיוון קדימה, בעוד שערך חיובי מייצג כוח מניע לתהליך בכיוון ההפוך. כאשר Δ G rxn הוא אפס, כוחות ההנעה קדימה ואחורה שווים, והתהליך מתרחש בשני הכיוונים באותו קצב (המערכת נמצאת בשיווי משקל). נזכיר ש-Q הוא הערך המספרי של ביטוי הפעולה במסה עבור המערכת, וניתן להשתמש בערכו כדי לזהות את הכיוון שאליו תתנהל תגובה על מנת להגיע לשיווי משקל. כאשר Q קטן מקבוע שיווי המשקל, K, התגובה תתקדם בכיוון קדימה עד שיושג שיווי משקל ו-Q = K. לעומת זאת, אם Q &gt; K, התהליך ימשיך בכיוון ההפוך עד להשגת שיווי המשקל. שינוי האנרגיה החופשית לתהליך המתרחש עם מגיבים ומוצרים הנמצאים בתנאים לא סטנדרטיים (לחצים שאינם 100 kPa; ריכוזים שאינם 1 M) קשור לשינוי הסטנדרטי של האנרגיה החופשית לפי משוואה זו: <img alt="Eq2" src="/files/ftp_upload/11694/11694%20PT%20eq%202.svg" style="text-align: center; height: 18px;"> R הוא קבוע הגז (8.314 J/K מול), T הוא הקלווין או הטמפרטורה המוחלטת, ו-Q הוא מנת התגובה. עבור מערכת בשיווי משקל, Q = K ו-ΔG = 0, וניתן לכתוב את המשוואה הקודמת כ <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;"> צורה זו של המשוואה מספקת קישור שימושי בין שתי התכונות התרמודינמיות החיוניות הללו, וניתן להשתמש בה כדי להפיק את קבועי שיווי המשקל משינויי אנרגיה חופשית סטנדרטיים ולהיפך. היחסים בין שינויים סטנדרטיים באנרגיה חופשית לבין קבועי שיווי משקל מסוכמים להלן. אם K &gt; 1, ΔG° &lt; 0 והתוצרים נמצאים בשפע יותר בתערובת התגובה. אם K &lt; 1, ΔG° &gt; 0 והמגיבים נמצאים בשפע יותר בתערובת התגובה. אם K = 1, ΔG° = 0 והמגיבים והתוצרים נמצאים בשפע באופן דומה בתערובת התגובה. הטקסט הזה מותאם מ <a href="https://openstax.org/books/chemistry-2e/pages/16-4-free-energy"> Openstax, Chemistry 2e, Section 16.4: Free Energy. </a>   </div>

הספונטניות של תהליך תלויה בטמפרטורה של המערכת. מעברי פאזה, למשל, יתקדמו באופן ספונטני בכיוון אחד או ...

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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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gibbs free energy and thermodynamic favorability

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...

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bond dissociation energy and activation energy

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How Bond Strength Shapes Reaction Speed

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How Temperature Changes Reaction Rate

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Dynamic Equilibrium

A reversible chemical reaction represents a chemical process that proceeds in both forward (left to right) and reverse (right to left) directions. When ...

Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.  Clarification Statement: Chemistry: Examples of chemical reactions could include the reaction of sodium and chlorine, carbon and oxygen, or carbon and hydrogen. Reaction classification aids in the prediction of products (e.g. synthesis, decomposition, single displacement, double displacement, and acid-base).

HS-PS1-2

Intermolecular vs Intramolecular Forces

Intermolecular forces (IMF) are electrostatic attractions arising from charge-charge interactions between molecules. The strength of the intermolecular ...

comparison-between-electrical-and-gravitational-forces

Comparison Between Electrical And Gravitational Forces

There are four fundamental forces in nature: the gravitational force, the electromagnetic force, the strong nuclear force, and the weak nuclear force. To ...

intermolecular-forces-and-physical-properties

Intermolecular Forces and Physical Properties



Intermolecular forces are attractive forces that exist between molecules. They dictate several bulk properties, such as melting points, boiling points, ...

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Electric Field of Two Equal and Opposite Charges

Atoms generally contain the same number of positively and negatively charged particles, protons, and electrons. Hence, they are electrically neutral. ...

Electric Field

Consider two point charges, each exerting Coulomb force on the other. It is possible to describe the Coulomb interaction via an intermediate step by ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

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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