CHM 102 Sinex
Thermodynamics
Part 2
CHM 102 Sinex
Free EnergyG - Gibbs free energy - maximum possible
useful work at constant T and PG = H – TSOur predictive tool for reactions
G > 0 non-spontaneousG = 0 at equilibriumG < 0 spontaneous
For a spontaneous process:maximize entropy minimize energy
CHM 102 Sinex
Standard molar free energy of formation - Gof
Gof = 0 for free elements in standard state
CaCO3 (s) CaO (s) + CO2 (g)
Calculate free energy change for a reaction
Gof : -1129 kJ/mole -604 kJ/mole -394 kJ/mole
Is this a spontaneous reaction?
CHM 102 Sinex
G = H – TSCASE RESULT- the sign of GS > 0H < 0 Spontaneous at ALL temperatures
S > 0H > 0 Spontaneous at high temperatures
S < 0H < 0 Spontaneous at low temperatures
S < 0H > 0
Non-spontaneous at ANY temperature
CHM 102 Sinex
Is this reaction possible?CH4 (g) C (diamond) + 2H2 (g)
@298K CH4diamon
d H2
Hof (kJ/mole) -75 2 0
So (J/K-mole) 186 2 131Go
f (kJ/mole) -51 3 0
Calculate Horxn, So
rxn, and Gorxn
G = H-TS
CHM 102 Sinex
Can it rain diamonds on Neptune and Uranus?
Neptune/Uranusblue color – CH4
10-50GPa2000-3000K
Can the reaction become spontaneous?
G = 0 = H - TS
Teq = H/S (estimate)
CHM 102 Sinex
Hess’ Law
C (graphite) + O2 (g) CO2 (g) H1
C (graphite) + ½ O2 (g) CO (g) H2
CO (g) + ½ O2 (g) CO2 (g) H3
Can't run this reaction, you get CO and CO2
Reactions are additive!
CHM 102 Sinex
C (graphite) + O2 (g) CO2 (g) H1
CO (g) + ½ O2 (g) CO2 (g) H3
C (graphite) + O2 (g) CO2 (g) H1
CO2 (g) CO (g) + ½ O2 (g) -H3
C (graphite) + ½ O2 (g) CO (g) H2 = H1-H3
CHM 102 Sinex
Biological pathways
Glucose + HPO4-2 + H+ [glucose-6-phosphate]- + H2O
Important in the metabolism of glucose
Go’ = 13.8 kJ
Glucose + 6O2 CO2 + H2O
First step in glycolytic pathway:
Is this reaction spontaneous?
CHM 102 Sinex
Coupled reactionsGlucose + HPO4
-2 + H+ [glucose-6-phosphate]- + H2O
Go’ = 13.8 kJATP-4 + H2O ADP-3 + HPO4
-2 + H+
Go’ = -30.5 kJ
Glucose + ATP-4 [glucose-6-phosphate]- + ADP-3
Go’ = 13.8 + -30.5 = -16.7 kJ
CHM 102 Sinex
Free energy and the equilibrium
constantGo = -2.303RTlog KT - kelvin temperature
R - gas constant – 8.314 J/K-mole
Go > 0 K < 1 reactant favoredGo = 0 K = 1Go < 0 K > 1 product favored
CHM 102 Sinex
Diamonds are NOT forever!Cdiamond Cgraphite
Gof : 3 kJ/mole 0
Gorxn = 0 – 3 = -3 kJ
log K = Gorxn x 1000
-2.303 x 8.314 J/K-mole x 298 Klog K = 0.53 K = 100.53 = 3.4
very very very very slow kinetics