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

Zmiana energii swobodnej, czyli styl <span="kolor: rgb(0, 0, 0); rodzina czcionek: Roboto, RobotoDraft, Helvetica, Arial, bezszeryfowa; biały-znak: pre-wrap;">ΔG, konkretnej reakcji jest sumą standardowej energii swobodnej i RT razy logarytmu naturalnego stosunku stężeń produktów do reagentów.
Jeśli ΔG reakcji jest ujemne, wtedy reakcja postępuje do przodu. ΔG staje się mniej ujemne wraz ze spadkiem stężenia reagentów i wzrostem stężenia produktów.
Ostatecznie, ΔG jest równe zero, gdy reakcja osiąga równowagę, gdzie szybkość reakcji do przodu i do tyłu jest równa.
W stanie równowagi stosunek stężenia produktów i reagentów jest równy stałej równowagi, K.
Równanie można przegrupować, aby pokazać matematyczną zależność między stylem <span="kolor: rgb(0, 0, 0); rodzina czcionek: Roboto, RobotoDraft, Helvetica, Arial, bezszeryfowy; biały znak: wstępne zawijanie;">ΔG0 i K.

energia swobodna i równowaga

Free Energy and Equilibrium

Zmiana energii swobodnej procesu może być postrzegana jako miara jego siły napędowej. Ujemna wartość ΔG reprezentuje siłę napędową procesu w kierunku do przodu, natomiast wartość dodatnia reprezentuje siłę napędową procesu w kierunku odwrotnym. Gdy ΔG wynosi zero, siły napędowe do przodu i do tyłu są równe, a proces zachodzi w obu kierunkach z tą samą szybkością (układ jest w równowadze). 

 Iloraz reakcji Q jest wygodną miarą stanu układu równowagi. Q jest wartością liczbową wyrażenia działania masy dla układu i można ją wykorzystać do określenia kierunku, w którym będzie przebiegać reakcja, aby osiągnąć równowagę. Gdy Q jest mniejsze niż stała równowagi K, reakcja będzie przebiegać w kierunku do przodu, aż do osiągnięcia równowagi i Q = K. I odwrotnie, jeśli Q > K, proces będzie przebiegał w odwrotnym kierunku, aż do osiągnięcia równowagi. 

 Zmiana energii swobodnej w procesie zachodzącym z reagentami i produktami obecnymi w niestandardowych warunkach (ciśnienia inne niż 1 bar; stężenia inne niż 1 M) jest powiązana ze standardową zmianą energii swobodnej zgodnie z następującym równaniem: 

 ΔG = ΔG° + RT lnQ 

 R to stała gazowa (8,314 J/K mol), T to temperatura Kelvina lub temperatura bezwzględna, a Q to iloraz reakcji. W przypadku równowag w fazie gazowej stosuje się współczynnik reakcji oparty na ciśnieniu, QP. Do określenia równowagi fazy skondensowanej stosuje się współczynnik reakcji oparty na stężeniu, QC. 

 Dla układu w równowadze Q = K i ΔG = 0, a poprzednie równanie można zapisać jako: 

 0 = ΔG° + RT lnK (w równowadze) 

 ΔG° = −RT lnK 

 Ta postać równania zapewnia użyteczne powiązanie między tymi dwoma podstawowymi właściwościami termodynamicznymi i może być wykorzystana do wyprowadzenia stałych równowagi ze standardowych zmian energii swobodnej i odwrotnie.

 Ten tekst został zaadaptowany z podręcznika Openstax, Chemia 2e, <a href="https://openstax.org/books/chemistry-2e/pages/16-4-free-energy">Sekcja 16.4: </a><a href="https://openstax.org/books/chemistry-2e/pages/16-4-free-energyy">Darmowa energia</a>.

Energia swobodna i równowaga

Swobodna zmiana energii dla procesu może być postrzegana jako miara jego siły napędowej. Ujemna wartość ΔG stanowi siłę napędową dla ...

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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.

Free Energy and Reaction Direction

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Free Energy and Reaction Direction | JoVE K12

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JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

Free Energy and Reaction Direction

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