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These are lecture notes on Thermodynamics II for the course Chemistry 09-106: Modern Chemistry II at Carnegie Mellon University. The notes cover topics such as biological energy storage, criteria for spontaneous reactions, and Gibbs Free Energy. The notes include equations and concepts related to bond enthalpies, ∆H, and ∆G. The notes also cover driving forces for reactions, such as enthalpy and entropy. The notes include examples of reactions and their associated ∆H values.
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1) Biological energy storage
Concept Based on bond enthalpies, what would you predict ∆H to be for the above reaction? a) ∆H<0 b) ∆H=0 c) ∆H>0 d) can’t tell from information given
Concept Which of the following must be true, based on the experimental ∆H a)b) The bonds (OP and OH) are stronger in ATP and water, than in ADP and phosphoric acidThe bonds (OP and OH) are weaker in ATP and water, than in ADP and phosphoric acid
Enzyme
∆H = -20.92kJ/mol
2) Criteria for spontaneous reactions ∆Hfo^ (H 2 O(l) ) = -285.83 kJ/mol ; ∆Hfo^ (CO 2 (g)) = -393.51 kJ/mol; ∆Hfo^ ( MgO(s) ) = -601.70 kJ/mol Mg + ½ O 2 Æ MgO ∆H= -601.7 kJ/mole Mg + ½ CO 2 Æ MgO + C ∆H= -404.94 kJ/mole
Ba(OH) 2. 8H 2 O(s) + 2NH 4 Cl (^) (s) Æ 2 NH 3 (aq) + 10 H 2 O (^) (l)+ BaCl (^2) (aq) ∆H > 0
3) Gibbs Free Energy ∆G = ∆H – T∆S A process is spontaneous if ∆G < 0 Two driving forces for reactions: Enthalpy driven: ∆H < Entropy driven: ∆S > 0
Concept What is the sign of ∆S for the following processes a) ∆S > 0, S increases b) ∆S < 0, S decreases Solid Æ Liquid
Liquid Æ Gas
N reactantsN < M Æ M productsCO 2 (g) Æ^ CO^ (g) + ½ O 2 (g)
N > M H 2 C=CH 2 (aq) + Br (^2) (aq) Æ H 2 BrC-CBrH 2 (aq)
Break a bond
NaCl (^) (s) Æ Na + (aq) + Cl - (aq)
Desorption from a surface
Elongate a polymer molecule