The change of free energy in the transmission of electron pairs in the respiratory chain (1) The activity of water can be arbitrarily set to 1.0 for calculation;
(2) Because [H + ]=1M does not conform to the actual situation, and it is generally believed that [H + ]=10 -7 M (pH=7), in order to distinguish its symbol, it is written as △ G zero ′；
(3) For example, for reaction, since various components are not standard concentrations (1M), the actual concentration is substituted into the following formula, and its value △ G 'is a problem;
(4) In the conjugate reaction, pay attention to the sum of the changes of various component reactions;
(5) Replace △ G zero Change to use equilibrium constant （ K eq ）It is often very useful. 
Helmholtz Substituted into the formula δ of the first law Q =d U 10 δ W , then:
δ W ≤-(d U - T d s )
If the initial and final temperatures of the system are equal to the temperature of the environment, that is T one = T two = T Ring, then
δ W ≤-d(U-Ts）
order , A is called Helmholz free energy, also called Helmholz function, also called work function, which is obviously the state function of the system. It can be concluded that: δ W ≤-d A or W ≤-D A
The meaning of this formula is that Isothermal process Middle, one Closed system The maximum work that can be done is equal to the reduction of its Helmholtz free energy. Therefore, Helmholtz free energy can be understood as the ability of the system to do work under isothermal conditions. This is F It's called the work function. If the process is irreversible, the work done by the system is less than the reduction of Helmholtz free energy T The ring remains unchanged, and T one = T two =T-ring). It should also be noted that the Helmholtz free energy is the property of the system State function Therefore, the value of DF is only determined by the initial and final states of the system, and is related to the changing channel Independent (i.e reversible Is irrelevant). But only in the isothermal reversible process, the reduction of Helmholtz free energy (- DF) of the system is equal to the maximum work done. Therefore, the reversibility of the process can be judged by using. An important conclusion can also be drawn. If the system is isothermal and constant volume without other work, then - D A ≥ 0, where the equal sign is applicable to reversible processes, and the unequal sign is applicable to spontaneous irreversible processes, that is, under the above conditions, if the system is left to its own nature, regardless of it, the spontaneous change will always proceed in the direction of Helmholtz free energy reduction until it is reduced to the minimum value allowed in this case and reaches equilibrium. The system cannot automatically generate D A >0.
The Helmholtz free energy can be used to judge the direction of spontaneous change under the above conditions, which is why the Helmholtz free energy is also called isothermal isochore. Under isothermal reversible condition, - D A = W max The reduction of Helmholtz free energy of the system is equal to the maximum work done externally.
Gibbs free energy, also called Gibbs function, is an important parameter in thermodynamics G express [2] 。
It is defined as: G = U − TS + pV = H − TS ，
among U Is the internal energy of the system, T Is the temperature (absolute temperature, K), S Is entropy, p Is the pressure, V Is the volume, H Is enthalpy.
Gibbs free energy Differential form Yes: d G =− S d T + V d p + μ d N ， Where μ is Chemical potential That is to say, the average Gibbs free energy of each particle is equal to the chemical potential. How to judge Closed system Is there a spontaneous process within? Gibbs free energy This is one State function And the most commonly used one: the maximum useful work that can be done by a closed system under isothermal and isobaric conditions corresponds to the state function Gibbs free energy (sometimes referred to as free energy or Gibbs function, the symbol is G ）Change of. △ G = W ′ max
Having a superscript plus' ' W 'generic Meritorious work The subscript max indicates that its absolute value reaches the maximum. about chemical reaction , its Gibbs free energy change △ G can be measured by electrochemical method, namely: △ G =- nFE
Gibbs free energy curve of liquid phase and solid phase versus composition Gibbs free energy is the judgment of process spontaneity, and its size is equivalent to the maximum possible useful work of the system to the environment. Therefore, we can also say that Gibbs free energy is a measure of the ability of the system to do useful work, that is, the measure of system process spontaneity. However, don't forget that we have already made it clear that the Gibbs free energy is used to measure the maximum useful work of the system under the condition that the process occurring in the system is an isothermal isobaric process. If isothermal isochoric process or other processes occur, it needs to be discussed separately.
The system undergoes a spontaneous process, and the expansion work can be positive or negative.
In conclusion, the judgment of the spontaneous process of the system under isothermal and isobaric conditions is:
△ G <0, i.e. △ G <0, spontaneous process; △ G >0, the process is not spontaneous (the reverse process is spontaneous); △ G =0, reaching the equilibrium state. A spontaneous process. With the development of the process, △ G The absolute value of is gradually reduced, and the spontaneity of the process is gradually reduced until finally, △ G =0, balance reached.
For a chemical reaction, we can give its standard molar reaction enthalpy △ r H m Θ [θ represents the standard state (273K, 101kPa)], as well as its standard molar reaction free energy change △ r G m Θ 。
With thermodynamic energy change △ U Enthalpy change △ H It will not change greatly with the change of temperature and pressure. It is totally different. The free energy of reaction is △ r G m It will change greatly with the change of temperature and pressure. Therefore, 298.15K, △ under standard state, directly found or calculated from thermodynamic data sheet r G m Θ (298.15K) data cannot be used under other temperature and pressure conditions and must be corrected.
The thermodynamic theory can be used to derive T Gas pressure at temperature versus △ r G m Θ The correction formula for the influence of is:
J =∏( p i / p Θ ) v i
Where π is an operator, representing Continued product (For example, a one ×a two ×a three =∏a i ; i=1,2,3）， p Θ Is the standard pressure=100kPa, p i For various gases (and △ r G m (T) Corresponding), v i Is the metering coefficient of each gaseous substance in the chemical equation, so J It is the product of the ratio of the partial pressure of each gas to the standard pressure in the non-standard state with the power of the metering coefficient. If there is still solution in the system, the above formula should be changed to:
J=∏( p i / p Θ ) v i ·∏( c i / c Θ ) v i
If there is only solution in the system, the above formula should be changed to:
J=∏( c i /c Θ ) v i
For most chemical reactions, the effect of temperature on the free energy of reaction is much greater than that of the partial pressure (and concentration) of reactants. The free energy of various reactions can be obtained by experiment or thermodynamic theoretical calculation. If the standard molar free energy of reaction △ r G m Θ As the ordinate and the reaction temperature as the abscissa, it can be seen visually how temperature affects the standard free energy of a reaction.
The free energy of some reactions increases with the increase of temperature, while others decrease, and the slope of the curve is also different. Moreover, both experiments and theoretical derivation confirm that the free energy changes very close to the linear relationship with temperature. When the temperature range is not large, the linearization approximation will not produce too large deviation, which is equivalent to straightening the curve in the figure. With this approximation, the linear equation of the effect of temperature on the free energy of reaction can be obtained:
△ r G m Θ = a + bT
a The intercept of the straight line on the ordinate, and b is the slope of the straight line. The intercept and slope of the equation are derived from thermodynamic theory, and it is confirmed that the intercept is just the reaction enthalpy △ r H m Θ , the slope is just the change value △ of another state function S S Negative value of (△ r S m Θ ）：
△ r G m Θ =△ r H m Θ - T △ r S m Θ
Historically, the term "free energy" has been used differently in different disciplines.
In chemistry, free energy refers to Gibbs free energy G Means that the Helmholtz free energy is“ Helmholtz function ”, to show the difference. In physics, free energy refers to Helmholtz free energy A Means that the Gibbs free energy is“ Gibbs function ”, to show the difference. 
