Chemistry, The Central Science , 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten. Chapter 19 Chemical Thermodynamics. John D. Bookstaver St. Charles Community College St. Peters, MO 2006, Prentice Hall, Inc. First Law of Thermodynamics.
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Processes that are spontaneous in one direction are nonspontaneous in the reverse direction.
In a reversible process the system changes in such a way that the system and surroundings can be put back in their original states by exactly reversing the process.
S = SfinalSinitial
The second law of thermodynamics states that the entropy of the universe increases for spontaneous processes, and the entropy of the universe does not change for reversible processes.
In other words:
For reversible processes:
Suniv = Ssystem + Ssurroundings = 0
For irreversible processes:
Suniv = Ssystem + Ssurroundings > 0
These last truths mean that as a result of all spontaneous processes the entropy of the universe increases.
S = k lnW
where k is the Boltzmann constant, 1.38 1023 J/K.
S(g) > S(l) > S(s)
Generally, when a solid is dissolved in a solvent, entropy increases.
The entropy of a pure crystalline substance at absolute zero is 0.
Larger and more complex molecules have greater entropies.
Entropy changes for a reaction can be estimated in a manner analogous to that by which H is estimated:
S° = nS°(products) - mS°(reactants)
where n and m are the coefficients in the balanced chemical equation.
Suniverse = Ssystem + Ssurroundings
Suniverse > 0
At temperatures other than 25°C,
DG° = DH TS
How does G change with temperature?
Under any conditions, standard or nonstandard, the free energy change can be found this way:
G = G + RT lnQ
(Under standard conditions, all concentrations are 1 M, so Q = 1 and lnQ = 0; the last term drops out.)
0 = G + RT lnK
G = RT lnK
K = eG/RT