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Chapter 19 (Thermodynamics):
1
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Spontaneous processes may become un spontaneous at a different temperature
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e
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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
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Adiabatic, meaning an isolated system à q = 0
Isothermal, a system in which the temperature is constant à ΔT = 0
Isobaric, a system in which the pressure is constant à ΔP = 0
Isochoric, a system in which the volume is constant à ΔV = 0

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2
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Microstate: each possible different arrangement of an atom
Entropy is a state function, i
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DS = Sfinal - Sinitial
For a process occurring at constant temperature (an isothermal process), the change
in entropy is equal to the heat that would be transferred if the process were
reversible divided by the temperature: DS =

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! #$%
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Second Law of Thermodynamics: The second law of thermodynamics states that the
entropy of the universe increases for spontaneous (irreversible) processes, and the
entropy of the universe does not change for reversible processes
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Temperature is a measure of the average kinetic energy of the molecules in a
sample
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–Volume
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Entropy changes in Chemical Reactions
à Entropy and Physical States (the effect of states on entropy)
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Entropy increases with the freedom of motion of molecules
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In general, entropy increases when
–Gases are formed from liquids and solids;
–Liquids or solutions are formed from solids;
–The number of gas molecules increases;
–The number of moles increases (see point 1)
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Standard entropies (molar entropy values of substances in their standard states)
tend to increase with increasing molar mass
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Heat that flows into or out of the system changes the entropy of the surroundings
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Since DSsurroundings = – qsystem
and qsystem = DHsystem
This becomes:
DSuniverse = DSsystem + – DHsystem / T
Multiplying both sides by -T, we get
-TDSuniverse = DHsystem - TDSsystem

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à Gibb’s Free Energy:
-TDSuniverse is defined as the Gibbs free energy, DG
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Therefore, when DG is negative, a process is spontaneous
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3
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Analogous to standard enthalpies of formation are standard free energies of
formation, DG°
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Under any conditions, standard or nonstandard, the free energy change can be
found this way:
DG = DG° + RT lnQ

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(Under standard conditions, all

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