In a Chemistry book I read thatdSuniv = dSext + dSsyst
(the change in entropy of a system during a chemical reaction + the change in entropy of the environment = the change in entropy of the universe)
And alsodSext = - dH / T
(when a chemical reaction produces heat, it causes an increase in the entropy of the environment)dSuniv = - dG / T
(it's more difficult to understand why a change in the entropy of the universe is linked to dG which is called change in "free energy" or the "energy available for work")
And we have the well-known relation
dG = dH – TdS
(relation 4) (S is Ssyst)
The relations seem correct since if we change in relation 4, dH for – TdSext, we get
dG = - TdSext – TdSsyst = - T (dSext + dSsyst) = -TdSuniv , thus relation 3.
However, in the book "Bioenergetics" by Dr A. L. Lehninger (W. A. Benjamin, 1971), we read p.27
dG = dE – TdS
There are 2 differences with relation 4 :
1) S is Suniv instead of Ssyst
2) dE replaces dH
So I write dG = dE – TdSuniv
dE is said to be the change in "total energy" of the system.
What is the "total energy of the system"
Moreover, if we combine the books, we can write
dG = dH – TdSsys = dE - TdSuniv
dE = dH + TdSuniv – T dSsyst
dE = dH + T(dSuniv – dSsyst)
dE = dH + TdSext
since dSext = - dH / T (relation 2)
dE = dH + T(- dH / T)dE = dH – dH = 0
It's a puzzle to me. If you have some energy to spare in order to decrease my "informational entropy"… Thank you.