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Lecture Notes E: Thermodynamics II
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
5) Sign of ∆ S for some common processes
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
