1. Review Unit 7 (Chp 5,8,19): Thermodynamics (∆Ho, ∆So, ∆Go, K)
Chemistry, The Central Science, 10th edition
Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten
Review Unit 7 (Chp 5,8,19): Thermodynamics (∆Ho, ∆So, ∆Go, K)
John D. Bookstaver
St. Charles Community College
St. Peters, MO
 2006, Prentice Hall, Inc.

2. Changes in Internal Energy
Energy is transferred between the system and surroundings, as either heat (q) or work (w).
E = q + w
E = ?
E = (–) + (+)
Surroundings
E = +
System
q in (+)
q out (–)
E = q + w
w on (+)
w by (–)

3. + = Energy (E) Enthalpy (H) (kJ) Entropy (S) (J/K)
Free Energy (G) (kJ)
ΔH = ΔE + PΔV
internal work by
energy system
(KE + PE) (–w)
(disorder)
microstates
–T∆Suniv as: ΔHsys & ΔSsys at a T
dispersal of matter & energy at T
max work done by favorable rxn
ΔE = q + w
PΔV = –w
(at constant P)
K > 1 means –∆Gsys & +∆Suniv
∆Suniv = +
ΔH = q
(heat)
ΔS = ΔH T
ΔG = ΔH – TΔS
sys
sys
–T∆Suniv

4. Big Idea #5: Thermodynamics
Bonds break and form to lower free energy (∆G).
Systems are driven by a decrease in G (–∆G) by:
a decrease in enthalpy (–∆H), or
an increase in entropy (+∆S), or
both.

5. Chp. 5,8: Calculate ∆H (4 Ways)
1) Bond Energies
Hrxn = (BEreactants)  (BEproducts)
2) Hess’s Law
Hoverall = Hrxn1 + Hrxn2 + Hrxn3 …
3) Standard Heats of Formation (Hf )
H = nHf(products) – nHf(reactants)
4) Calorimetry (lab)
q = mc∆T (surroundings or thermometer)
–q = ∆H ∆H/mol = kJ/mol (molar enthalpy)
(NOT given)
(+ broken)
(– formed)
(NOT given)    
(given)
(given)

6. Entropy (S) (Molecular Scale)
S : dispersal of matter & energy at T
S(s) < S(l) < S(aq) < S(g)
(s) + (l)  (aq)
+∆S (dispersal)
gas
solid T
more microstates
Temperature
 Volume
 Particle mixing
 Particle number
 Particle size V
H2O(g)
H2O(g)
So = So(products) – So(reactants)
(given)

7. Thermodynamically Favorable
Chemical and physical processes are driven by:
decrease in enthalpy (–∆Hsys)
increase in entropy (+∆Ssys)
causes (+∆Ssurr)
(+)
(+)
Suniv = Ssystem + Ssurroundings > 0
Thermodynamically Favorable: (defined as)
increasing entropy of the universe (∆Suniv > 0)
∆Suniv > 0
(+Entropy of the Universe)

8. (∆Suniv) ↔ (∆Gsys) Hsystem
For all thermodynamically favorable reactions:
Suniverse = Ssystem + Ssurroundings > 0
(Boltzmann)
Hsystem T
Suniverse = Ssystem +
(Clausius)
multiplying each term by T:
–TSuniverse = –TSsystem + Hsystem
rearrange terms:
–TSuniverse = Hsystem – TSsystem
Gsystem = Hsystem – TSsystem
(Gibbs free energy equation)

9. (∆Suniv) & (∆Gsys) –TSuniv = Hsys – TSsys Gsys = Hsys – TSsys
(Gibbs free energy equation)
Gibbs defined TDSuniv as the change in
free energy of a system (Gsys) or G.
Free Energy (G) is more useful than
Suniv b/c all terms focus on the system.
If –Gsys , then +Suniverse . Therefore…
–G is thermodynamically favorable.
“Bonds break & form to lower free energy (∆G).”

10. Standard Free Energy (∆Go) and Temperature (T)
(on equation sheet)
(consists of 2 terms)
DG = DH – TS
free energy (kJ/mol)
enthalpy term (kJ/mol)
entropy term (J/mol∙K)
units convert to kJ!!!
max energy used for work
energy transferred as heat
energy dispersed as disorder
The temperature dependence of free energy comes from the entropy term (–TS).

11. Standard Free Energy (∆Go) and Temperature (T)
DG = DH  TS
Thermodynamic Favorability
∆Go =
(∆Ho)
∆So
– T( )
( ) –T( )
(high T) –
(low T) +
(fav. at high T)
(unfav. at low T) + + =
( ) – T ( ) + + –
(unfav. at ALL T) + =
( ) – T( ) +
(fav. at ALL T) – =
( ) – T( ) – +
(high T) +
(low T) –
( ) –T( )
(unfav. at high T)
(fav. at low T) – – =
( ) – T ( ) – –

12. Calculating ∆Go (4 ways)
Standard free energies of formation, Gf :
Gibbs Free Energy equation:
From K value (next few slides)
From voltage, Eo (next Unit)
DG = SG(products) – SG(reactants) f
(given equation)
DG = DH – TS
(given equation)
(may need to calc. ∆Ho & ∆So first)
(given equation)
(given equation)

13. Free Energy (∆G) & Equilibrium (K)
G = –RT ln K
(on equation sheet)
If G in kJ,
then R in kJ………
R = J∙mol–1∙K–1
= kJ∙mol–1∙K–1
–∆Go RT
= ln K
–∆Go RT
Solved for K :
(NOT on equation sheet)
K = e^

14. Free Energy (∆G) & Equilibrium (K)
G = –RT ln K
∆Go = –RT(ln K) K
@ Equilibrium – + =
–RT ( )
> 1
product favored
(favorable forward) + – =
–RT ( )
< 1
reactant favored
(unfavorable forward)