Basics Boltzmann Explanation
A Spontaneous processes tend to occur * Atom or molecule can possess only certain * Energy distribution at higher temps - more
naturally under a set of conditions values of energy energy lvls accessible
A Nonspontaneous processes need N A At T 0 molecules distributed over available
7 A More microstates - higher entropy
external input of energy to occur energy levels
Classic Approach to Entropy S =
RBInW
A Entropy change of system is heat transferred S entropy
i
=
to system divided by system temp W = no of microstates
Grev RB Boltzmann
= constant
&S =
T
↳ rev heat gained or lost
= Microstates are ways in which molecules
Li T =
absolute temp of system can be arranged while keeping A Config 3 has most no of states so most
total energy constant probable
N
T
Direction of Spontaneous Changes
↓ Y
Molecular Approach How do the Approaches Relate?
D Higher dispersion/distribution of A Change in extent to which energy is dispersed depends on
energy, more choice, more ways to how much energy is transferred as heat
store energy, more possible states - * Heat stimulates random motion in surroundings, work
higher entropy stimulates uniform motion so no change entropy
S RBInw
=
-" &S =
quest
A Molecules with high T - large no of energy lvls so small grev
↳ small change in available lvls
A Molecules with low T - small no of energy lvls so small 9new
* Energy lvls are closer together at higher LDbig change in available lvls
volume - due to decrease in motion restriction
A Greater numbers of possible arrangements of * Change in entropy upon heating will be greater when
molecular energies on additional lvls energy transferred to cold body than when transferred to
↳ More microstates hot body
, Basics Spontaneity of Chem Reactions
A Entropies of all perfectly crystalline * Consider change in surroundings * If a reaction of phase transition occurs
substances are the same at T g =
A Heat transferred onto them can be identified at constant pressure then,
* S(0) 8 for all perfectly crystalline materials
= w/ their enthalpy (state function) AH
AS -
=
A Defined as diff btwn molar entropies of pure,
Asar =Eur
sur T
AS sur =
separated products and pure, separated
reactants, all in standard states at specific temp A If a process is exothermic, AH is
* Usually have info on heat supplied or negative and ASsur is positive
ArS
= up
VSm- escaping our system so, * Entropy of surrounding increases when
q heat transferred into them
& Assur = -
T
* Total change in entropy for
reversible process is zero
1
3rd Law of Thermodynamics
L
Gibbs Energy -
A Way to express total change in entropy of system Examples
and its surroundings using properties of system Determine standard rxn entropy, at 25 Calculate standard Gibbs energy of
LD If T is constant: deg, for following spontaneous rxn: rxn at 25 deg for:
AG TAS
SH
N2(g) 3Hz(g) >
2NHy1g) (O1g1
1
120x(g) CO2g,
-
=
+ -
+ -
↳ If T and p are constant:
AG TAS
AfG((z(y) [Af4 ((Digi) 2004 %02191)]
°
= -
total - 1H DrGo = -
+
AS sur =
T -
= 394 4 . -
1 137 2
- .
+ 0)
A If at constant T&p, changes in Gibbs energy of a =
92280/mol =
=
257 2R)mol.
-
system is proportional to overall change in entropy of 298 15k
.
system plus surroundings =
3096K "mol-
* In spontaneous process at constant T&p, Gibbs energy
decreases ArStora - 201
= + 309
= 1086K "mol-
A Spontaneous processes tend to occur * Atom or molecule can possess only certain * Energy distribution at higher temps - more
naturally under a set of conditions values of energy energy lvls accessible
A Nonspontaneous processes need N A At T 0 molecules distributed over available
7 A More microstates - higher entropy
external input of energy to occur energy levels
Classic Approach to Entropy S =
RBInW
A Entropy change of system is heat transferred S entropy
i
=
to system divided by system temp W = no of microstates
Grev RB Boltzmann
= constant
&S =
T
↳ rev heat gained or lost
= Microstates are ways in which molecules
Li T =
absolute temp of system can be arranged while keeping A Config 3 has most no of states so most
total energy constant probable
N
T
Direction of Spontaneous Changes
↓ Y
Molecular Approach How do the Approaches Relate?
D Higher dispersion/distribution of A Change in extent to which energy is dispersed depends on
energy, more choice, more ways to how much energy is transferred as heat
store energy, more possible states - * Heat stimulates random motion in surroundings, work
higher entropy stimulates uniform motion so no change entropy
S RBInw
=
-" &S =
quest
A Molecules with high T - large no of energy lvls so small grev
↳ small change in available lvls
A Molecules with low T - small no of energy lvls so small 9new
* Energy lvls are closer together at higher LDbig change in available lvls
volume - due to decrease in motion restriction
A Greater numbers of possible arrangements of * Change in entropy upon heating will be greater when
molecular energies on additional lvls energy transferred to cold body than when transferred to
↳ More microstates hot body
, Basics Spontaneity of Chem Reactions
A Entropies of all perfectly crystalline * Consider change in surroundings * If a reaction of phase transition occurs
substances are the same at T g =
A Heat transferred onto them can be identified at constant pressure then,
* S(0) 8 for all perfectly crystalline materials
= w/ their enthalpy (state function) AH
AS -
=
A Defined as diff btwn molar entropies of pure,
Asar =Eur
sur T
AS sur =
separated products and pure, separated
reactants, all in standard states at specific temp A If a process is exothermic, AH is
* Usually have info on heat supplied or negative and ASsur is positive
ArS
= up
VSm- escaping our system so, * Entropy of surrounding increases when
q heat transferred into them
& Assur = -
T
* Total change in entropy for
reversible process is zero
1
3rd Law of Thermodynamics
L
Gibbs Energy -
A Way to express total change in entropy of system Examples
and its surroundings using properties of system Determine standard rxn entropy, at 25 Calculate standard Gibbs energy of
LD If T is constant: deg, for following spontaneous rxn: rxn at 25 deg for:
AG TAS
SH
N2(g) 3Hz(g) >
2NHy1g) (O1g1
1
120x(g) CO2g,
-
=
+ -
+ -
↳ If T and p are constant:
AG TAS
AfG((z(y) [Af4 ((Digi) 2004 %02191)]
°
= -
total - 1H DrGo = -
+
AS sur =
T -
= 394 4 . -
1 137 2
- .
+ 0)
A If at constant T&p, changes in Gibbs energy of a =
92280/mol =
=
257 2R)mol.
-
system is proportional to overall change in entropy of 298 15k
.
system plus surroundings =
3096K "mol-
* In spontaneous process at constant T&p, Gibbs energy
decreases ArStora - 201
= + 309
= 1086K "mol-
