Helmholtz free energy 玄姆霍兹( von helmholz,HLP,1821~1894 德国人)定义了一个状态函数 def A称为 Helmholz free energy,是状态函数,具有容量性质。 da -dU-d(ts)=dU-Tas=dU-dQrey =8W dU=6O+6W=60+δW rev rev dU-bQrey= aWre da=ow 4上一内容下一内容◇回主目录 返回 2021/2/22
上一内容 下一内容 回主目录 返回 2021/2/22 Helmholtz free energy 亥姆霍兹（von Helmholz, H.L.P.,1821~1894, 德国人）定义了一个状态函数 def A U TS − A称为Helmholz free energy，是状态函数，具有容量性质。 dA =dU-d(TS) = dU-TdS=dU-Qrev T dU=Q+ W =Qrev +Wrev dU- Qrev= Wrev = Wrev dA=Wrev
Gibbs Free Energy Some remarks on the gibbs function The gibbs function is more common in chemistry than the helmholtz function This is because we are usually more interested in the conditions of equilibrium and the direction of chemical change when systems are at constant pressure rather than constant volume Now dRey consists of expansion work and possibly some other kind of work 4上一内容下一内容令回主目录 返回 2021/2/22
上一内容 下一内容 回主目录 返回 2021/2/22 Gibbs Free Energy def G H TS − Some remarks on the Gibbs function. The Gibbs function is more common in chemistry than the Helmholtz function. This is because we are usually more interested in the conditions of equilibrium and the direction of chemical change when systems are at constant pressure rather than constant volume. Now dWrev consists of expansion work and possibly some other kind of work
dG-dh- Tds - Sdt dH=dU+d(pv) =8Q+SWe +oM+ pdv +vdp (8we=-pdv) 8Q+SWf +vdp 所以dG=8+8W+四p-7dS-SdT =6W fmax (dT=0,dp=0可逆) 或 (gPr=-omf max This means that under conditions of constant pressure and temperature the change of the gibbs function between specified states gives the maximum work available from that process other than expansion work 4上-内容下一内容◆回主目录 返回 2021/2/22
上一内容 下一内容 回主目录 返回 2021/2/22 dG=dH – TdS – SdT dH=dU+d(pV) = + + + + Q W W p V V p e f d d = + + Q W V p f d = Wf,max ( dT = 0,dp = 0, 可逆） 所以 d d d d G Q W V p T S S T = + + − − f , ,R f,max ( d ) 或 − = − G W T p This means that under conditions of constant pressure and temperature the change of the Gibbs function between specified states gives the maximum work available from that process other than expansion work. e ( d ) = − W p V
The criterion of Gibbs free energy At constT,P,W=0, closed sys (-dG) ≥0 T,p,wf=0 or (dG)pm=0≤0 When we want to know whether a reaction wil tend to go in a particular direction(the pressure and temperature being constant)we have to determine ag for the reaction △G=G products G reactants 4上一内容下一内容令回主目录 返回 2021/2/22
上一内容 下一内容 回主目录 返回 2021/2/22 The criterion of Gibbs free energy At const.T, P, W`=0, closed sys.. ( d ) , , 0 0 f − G T p W = (d ) , , 0 0 f or G T p W = When we want to know whether a reaction will tend to go in a particular direction (the pressure and temperature being constant) we have to determine G for the reaction: G =G products – G reactants
Initial state (reactants)>final state( If this ag is negative, then the reaction has a natural tendency to move spontaneously from reactants to proaucts If Ag is positive then the reaction as written will not proceed spontaneously but the reverse reaction will be the spontaneous one 4上一内容下一内容令回主目录 返回 2021/2/22
上一内容 下一内容 回主目录 返回 2021/2/22 Initial state (reactants)→ final state(… If this G is negative, then the reaction has a natural tendency to move spontaneously from reactants to products. If G is positive, then the reaction as written will not proceed spontaneously, but the reverse reaction will be the spontaneous one