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

A mudança de energia livre, ou ΔG, de uma reação particular é a soma da energia livre padrão e RT vezes o log natural da razão entre as concentrações de produtos e reagentes.
Se o ΔG de uma reação é negativo, então a reação progride. O ΔG torna-se menos negativo à medida que as concentrações dos reagentes diminuem e as dos produtos aumentam.
Eventualmente, o ΔG é igual a zero quando a reação atinge o equilíbrio, onde as taxas de reação direta e reversa são iguais.
No equilíbrio, a razão entre a concentração de produtos e reagentes é igual à constante de equilíbrio, K.
A equação pode ser reorganizada para mostrar a relação matemática entre ΔG0 e K.

energia livre e equilíbrio

Free Energy and Equilibrium

A mudança de energia livre para um determinado processo pode ser vista como uma medida de sua força motriz. Um valor negativo para ΔG representa uma força motriz para o processo na direção direta, enquanto um valor positivo representa uma força motriz para o processo na direção reversa. Quando ΔG é zero, as forças motrizes direta e reversa são iguais e o processo ocorre em ambas as direções na mesma taxa (o sistema está em equilíbrio). 

 O quociente de reação, Q, é uma medida conveniente do estado de um sistema em equilíbrio. Q é o valor numérico da expressão de ação de massa para o sistema e pode ser usado para identificar a direção na qual uma reação ocorrerá para atingir o equilíbrio. Quando Q é menor que a constante de equilíbrio, K, a reação prosseguirá na direção direta até que o equilíbrio seja alcançado e Q = K. Por outro lado, se Q > K, o processo prosseguirá na direção inversa até que o equilíbrio seja alcançado. 

 A mudança de energia livre para um processo que ocorre com reagentes e produtos presentes sob condições não padronizadas (pressões diferentes de 1 bar; concentrações diferentes de 1 M) está relacionada à mudança de energia livre padrão de acordo com esta equação: 

 ΔG = ΔG° + RT lnQ 

 R é a constante do gás (8,314 J/K mol), T é a temperatura em Kelvin, ou temperatura absoluta, e Q é o quociente de reação. Para equilíbrios em fase gasosa, é utilizado o quociente de reação baseado em pressão, QP. O quociente de reação baseado em concentração, QC, é usado para equilíbrio de fase condensada. 

 Para um sistema em equilíbrio, Q = K e ΔG = 0, e a equação anterior pode ser escrita como: 

 0 = ΔG° + RT lnK (em equilíbrio) 

 ΔG° = −RTlnK 

 Esta forma da equação fornece uma ligação útil entre estas duas propriedades termodinâmicas essenciais e pode ser usada para derivar constantes de equilíbrio a partir de mudanças padrão de energia livre e vice-versa.

 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 Livre e Equilíbrio

A mudança de energia livre para um processo pode ser vista como uma medida de sua força motriz. Um valor negativo para ΔG representa uma força motriz para o ...

Education

JoVE Core

Cell Biology

Biologia Celular

Unit 1

Unidade 1

Energy and Catalysis

Energia e Catálise

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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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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 - Biologia Celular ilustra processos celulares complexos em vídeos de animação fáceis de entender e, ao mesmo tempo, abrangentes. Esta coleção foca nos componentes e funções essenciais das células, incluindo organelas e membranas, transporte celular e energia celular. É complementado por vídeos de Cientistas em ação que demonstram a aplicação da biologia celular em experimentos de pesquisa do mundo real.

Free Energy and Reaction Direction

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