Name: free energy and reaction direction
Uploaded: 2023-04-30T10:09:12.000Z
Duration: 55 s
Channel: JoVE

自由エネルギーの変化、またはΔG, は、標準自由エネルギーとRTの合計に、生成物と反応物の濃度の比率の自然対数を掛けたものです。
ΔGが負の場合、反応は進行します。ΔGは、反応物の濃度が減少し、生成物の濃度が増加するにつれて、負が少なくなります。
最終的に、ΔGは、反応が平衡に達したときにゼロに等しくなります。ここで順方向と逆方向の反応速度が等しくなります。
平衡状態では、生成物と反応物の濃度の比は平衡定数Kに等しくなります。 
この方程式は、ΔG 0 と K の間の数学的な関係を示すように並べ替えることができます。

自由エネルギーと平衡

Free Energy and Equilibrium

プロセスの自由エネルギー変化は、その推進力の尺度として見ることができます。 ΔＧの負の値は順方向のプロセスの駆動力を表し、正の値は逆方向のプロセスの駆動力を表す。 ΔG がゼロの場合、順方向と逆方向の駆動力は等しく、プロセスは両方向に同じ速度で発生します (システムは平衡状態にあります)。

反応商 Q は、平衡系の状態を表す便利な尺度です。 Q は系の質量作用表現の数値であり、平衡に達するために反応が進む方向を特定するために使用できます。 Q が平衡定数 K より小さい場合、反応は平衡に達し Q = K になるまで順方向に進みます。逆に、Q > K の場合、プロセスは平衡に達するまで逆方向に進みます。

非標準条件（1 バール以外の圧力、1 M 以外の濃度）下で存在する反応物および生成物を使用して発生するプロセスの自由エネルギー変化は、次の方程式に従って標準自由エネルギー変化に関連します。

ΔG = ΔG° + RT lnQ

R は気体定数 (8.314 J/K mol)、T はケルビンまたは絶対温度、Q は反応商です。 気相平衡の場合、圧力に基づく反応商 QP が使用されます。 濃度ベースの反応商 QC は、凝縮相の平衡に使用されます。

平衡状態にあるシステムの場合、Q = K および ΔG = 0 であり、前の式は次のように書くことができます：

0 = ΔG° + RT lnK (平衡時)

ΔG° = −RT lnK

この形式の方程式は、これら 2 つの必須の熱力学特性間の有用な関連を提供し、標準自由エネルギー変化から平衡定数を導出したり、その逆に平衡定数を導出したりするために使用できます。

このテキストは Openstax, Chemistry 2e から引用したものです <a href="https://openstax.org/books/chemistry-2e/pages/16-4-free-energy">Section 16.4: Free Energy.</a>

プロセスの自由エネルギー変化は、その駆動力の尺度と見なすことができます。ΔGの負の値は、...

Education

JoVE Core

Cell Biology

細胞生物学

Unit 1

ユニット1

Energy and Catalysis

エネルギーと触媒

KEY TERMS AND CONCEPTS

主要用語と概念

free energy and reaction direction

Free energy and reaction direction are linked in chemical equilibrium. A free energy change, ΔG, shows the driving force for a process. When ΔG is negative, the process is driven forward. When ΔG is positive, the reverse direction is favored. When ΔG is zero, the forward and reverse driving forces are equal, and the system is at equilibrium.

The reaction quotient, Q, helps show how close a system is to equilibrium. Q is the numerical value of the mass action expression for the system. It can be used to predict which way a reaction will shift to reach equilibrium. If Q is less than the equilibrium constant, K, the reaction proceeds forward until Q = K. If Q is greater than K, the process shifts in reverse until equilibrium is reached.

For reactions under nonstandard conditions, ΔG depends on both the standard free energy change and the reaction quotient. The relationship is ΔG = ΔG° + RT ln Q, where R is the gas constant, T is temperature in kelvin, and Q is the reaction quotient. For gas-phase equilibria, the pressure-based quotient QP is used. For condensed-phase equilibria, the concentration-based quotient QC is used.

At equilibrium, Q = K and ΔG = 0. Substituting that condition into the equation gives 0 = ΔG° + RT ln K. This can be rearranged to ΔG° = −RT ln K. That link lets chemists find an equilibrium constant from a standard free energy change, or find a standard free energy change from K.

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key terms and concepts

Learn how free energy change, reaction quotient, and equilibrium constant work together to show reaction direction and equilibrium in chemistry.

Free Energy and Reaction Direction | JoVE K12

cell biology

JoVE Core 細胞生物学は、複雑な細胞プロセスを、わかりやすく包括的なアニメーション ビデオ レッスンで説明します。このコレクションは、細胞小器官や膜、細胞輸送、細胞のエネルギー学など、細胞の必須コンポーネントと機能に焦点を当てています。これは、実際の研究実験における細胞生物学の応用を実証する科学者による実際のビデオによって補足されています。

Free Energy and Reaction Direction

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