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

Gibbs 자유 에너지 또는 델타 G의변화는 에너지 저장 채권이 각각 형성되거나 파손될 때 흡수되거나 방출되는 에너지입니다.
델타 G의 표시는 엔탈피, 엔트로피 및 온도의 징후와 상대적 값에 따라 달라집니다.
델타 H가 음수이고 델타 S가 양수인 경우 델타 G는 모든 온도에서 음수입니다. 따라서, 시스템의 엔트로피가 증가하는 퇴근 반응은 항상 자발적이다.
델타 H와 델타 S가 모두 음수인 경우 델타 G는 온도에 따라 다릅니다. 부정적인 엔탈피와 엔트로피 변화에 대한 반응은 저온에서만 자발적입니다.
델타 G는 델타 H와 델타 S가 모두 양수인 경우 온도에 따라 달라집니다. 긍정적 인 엔탈피와 엔트로피 변화와 반응은 더 높은 온도에서만 자발적입니다.
델타 H가 긍정적이고 델타 S가 음수일 때 델타 G는 항상 긍정적이며 반응은 모든 온도에서 비자발적입니다.
임의의 반응 혼합물 조성물에 대해, 반응에 대한 델타 G는 표준 자유 에너지및 RT 배의 합으로 반응 지수의 천연 로그를 한다.
반응제와 제품이 평형에 있을 때, 자유 에너지 변화는 0이고 반응 지수는 평형 상수와 같습니다. 따라서 표준 자유 에너지 변화는 음의 RT ln(K)과 같습니다.
델타 G naught가 0 미만인 경우 ln(K)은 양성이며, 이는 K가 1보다 크다는 것을 의미합니다. 이 경우 제품 형성이 평형에 선호됩니다. 평형 상수가 클수록 깁스 자유 에너지의 감소가 커진다.
음의 델타 G 값을 가진 반응은 주변에 자유 에너지의 방출을 포함하고 'exergonic'반응이라고합니다.
반대로, 델타 G naught가 0보다 크면 ln(K)이 음수이며, K가 1 미만이며 반응의 역방향이 선호된다.
양극삼각주 G의 반응은 주변환경의 자유로운 에너지를 흡수하며 '엔더고닉' 반응이라고 합니다.

깁스 자유에너지와 열역학적 호감도

과정의 자발성은 시스템 온도에 따라 달라집니다. 예를 들어, 상전이는 해당 물질의 온도에 따라 한 방향 또는 다른 방향으로 자발적으로 진행됩니다. 마찬가지로 일부 화학 반응은 온도에 따른 자발성을 나타낼 수도 있습니다. 이 개념을 설명하기 위해 공정의 엔탈피 및 엔트로피 변화에 대한 자유 에너지 변화와 관련된 방정식이 고려됩니다.


<img alt="Eq1" src="/files/ftp_upload/11694/11694%20PT%20eq%201.svg" style="text-align: center; height: 15px;">

자유 에너지 변화의 산술 부호에 반영된 과정의 자발성은 엔탈피 및 엔트로피 변화의 부호와 어떤 경우에는 절대 온도에 의해 결정됩니다. T는 절대(켈빈) 온도이므로 양수 값만 가질 수 있습니다. 따라서 엔탈피 및 엔트로피 변화의 징후와 관련하여 네 가지 가능성이 존재합니다.


<ul style="list-style-type: disc; display: flex; flex-direction: column; gap: 10px; padding: 0 0 0 40px;">
<li>
 ΔH와 ΔS는 모두 양수입니다. 이 조건은 시스템 엔트로피의 증가와 관련된 흡열 과정을 설명합니다. 이 경우 TΔS 항의 크기가 ΔH보다 크면 ΔG는 음수가 됩니다. TΔS 항이 ΔH보다 작으면 자유 에너지 변화는 양수입니다. 이러한 과정은 고온에서는 자발적이고 저온에서는 비자발적입니다.
</li> 
<li>ΔH와 ΔS는 모두 음수입니다. 이 조건은 시스템 엔트로피 감소와 관련된 발열 과정을 설명합니다. 이 경우 TΔS 항의 크기가 ΔH보다 작으면 ΔG는 음수가 됩니다. TΔS 항의 크기가 ΔH보다 크면 자유 에너지 변화는 양수입니다. 이러한 과정은 저온에서는 자발적이고 고온에서는 비자발적입니다.
</li>
<li>ΔH는 양수이고 ΔS는 음수입니다. 이 조건은 시스템 엔트로피의 감소를 포함하는 흡열 과정을 설명합니다. 이 경우 ΔG는 온도에 관계없이 양의 값을 갖습니다. 이러한 과정은 모든 온도에서 비자발적입니다.
</li>
<li>ΔH는 음수이고 ΔS는 양수입니다. 이 조건은 시스템 엔트로피의 증가와 관련된 발열 과정을 설명합니다. 이 경우 ΔG는 온도에 관계없이 음수가 됩니다. 이러한 과정은 모든 온도에서 자발적입니다.
</li> 
</ul>

과정의 자유 에너지 변화는 과정의 추진력을 측정하는 것으로 볼 수 있습니다. ΔG의 음수 값은 정방향 과정의 추진력을 나타내고, 양수 값은 역방향 과정의 추진력을 나타냅니다. ΔGrxn 이 0이면 정방향 및 역뱡항 추진력이 동일하고 반응 과정은 양방향에서 동일한 속도로 발생합니다(시스템의 평형 상태).

Q는 시스템의 질량 작용 표현식의 수치 값이며, 그 값은 평형을 달성하기 위해 반응이 진행되는 방향을 식별하는 데 사용될 수 있습니다. Q가 평형 상수 K보다 작으면 반응은 평형에 도달하고 Q = K가 될 때까지 정방향으로 진행됩니다. 반대로, Q &gt; K이면 평형에 도달할 때까지 반응은 역방향으로 진행됩니다.


비표준 조건(100kPa 이외의 압력, 1M 이외의 농도)에서 반응물과 생성물이 존재하는 과정에서 발생하는 반응의 자유 에너지 변화는 다음 방정식에 따른 표준 자유 에너지 변화와 관련됩니다.


<img alt="Eq2" src="/files/ftp_upload/11694/11694%20PT%20eq%202.svg" style="text-align: center; height: 18px;">

R은 기체 상수(8.314 J/K mol), T는 켈빈 또는 절대 온도, Q는 반응 지수입니다. 평형 상태의 시스템에 대해 Q = K 및 ΔG = 0이며 이전 방정식은 다음과 같이 쓸 수 있습니다.


<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;">

이러한 형태의 방정식은 두 가지 필수 열역학적 특성 사이의 유용한 연결을 제공하며 표준 자유 에너지 변화로부터 평형 상수를 유도하는 데 사용될 수 있으며 그 반대의 경우도 마찬가지입니다. 표준 자유 에너지 변화와 평형 상수 사이의 관계는 아래에 요약되어 있습니다.



K &gt; 1이면 ΔG° &lt; 0이고 생성물은 반응 혼합물에 더 풍부합니다. 
K &lt; 1이면 ΔG° &gt; 0이고 반응물은 반응 혼합물에 더 풍부합니다. 
K = 1이면 ΔG° = 0이고 반응물과 생성물은 반응 혼합물에 비교적 풍부합니다.


이 문서는에서 발췌되었습니다. <a href="https://openstax.org/books/chemistry-2e/pages/16-4-free-energy">Openstax, Chemistry 2e, Section 16.4: Free Energy.</a>

프로세스의 자발성은 시스템의 온도에 따라 다릅니다. 예를 들어, 상전이는 한 방향으로 자발적으로 진행되거나 ...

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주요 용어 및 개념

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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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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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, ...

electric-field-of-two-equal-and-opposite-charges

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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