1. TERMS & DEFINITIONS Bond dissociation E: endo/exo thermic: Exergonic: Endergonic: E required to break a bond; single weakest, triple strongest absorb heat, +G release heat, -G spont. rxn; release free E; -G nonspont. rxn; absorb free E; +G Heat of Reaction, ENTHALPY; diff. bet. E sums: bonds broken - bonds formed Gibbs E, Free E Measure of disorder, ENTROPY http://www.learnerstv.com/animation/animation.php?ani=120&cat=Chemistry

2. Activation E: Reaction Rate: Catalyst: E barrier; E level in which the reactants have to overcome for the rxn to proceed forward; E act The speed at which the rxn takes place Subst. that increases the rxn speed; does not combine with any rxn subst. E Rxn progress without catalyst with catalyst

3. --- + always --- Spont @ all temps; 2 O 3 (g) ----> 3 O 2 (g) reverse always nonspont. + --- always + Nonspont @ all temps; 3 O 2 (g) ----> 2 O 3 (g) reverse rxn occurs --- --- -- low temp Spont @ low temps; CaO (s) + CO 2 (g) ----> + hi temp reverse nonspont CaCO 3 (s) + + + low temp Nonspont @ low temps; CaCO 3 (s) ----> CaO (s) + -- hi temp becomes spont as temp CO 2 (g) increases RXN characteristics Example

4. @ high temps, T S is large, value bigger than H, - G, thus, exothermic Amount of E, H for reverse rxn is same value as forward rxn, but opposite sign To manufacture sulfuric acid, a key step is the oxidation of sulfur dioxide with oxygen to sulfur trioxide. Calculate G at 298 K when H = -198.4 kJ & S = -187.8 J/K S = -.1878 kJ/K = -198.4 kJ – (-55.96 kJ) = -198.4 kJ + 55.96 kJ G = -142.44 kJ

5. E RXN. PROCEEDS reactants products reactants products

6. E RXN. PROCEEDS reactants products reactants

7. Rxn progress E slower rxn faster rxn less stable intermediates more stable intermediates faster rxn slower rxn less stable intermediates more stable intermediates Rxn. E diagrams for 2 similar competing reactions

8. EQUILIBRIUM CONSTANT Symbol: [ ] brackets indicate concentration At equilibrium: rate fwd = rate rev What is needed? 1. balanced eqn 2. concentrations of all substs.

9. In General Eqn: a A (s) + b B (aq) ----  c C (aq) + d D (g) The ratio, @ equil, of the concentrations of products raised to their stoichiometric coeff. divided by concentrations of reactants raised to their stoichiometric coeff.

10. Suppose a mixture of H 2 & I 2 reach equilibrium at 445 o C. The equilibrium Concentrations are [H 2 ] = 0.11 M, [I 2 ] = 0.11 M, and [HI] = 0.78 M. What is the equilibrium constant? Eqn: H 2 (g) + I 2 (g) -------  2 HI (g) = 50.28

11. Meaning K eq 1.K eq << 1 Reverse rxn is favored; fwd rxn not proceed very far; at equil. more reactants present than pdts 2.K eq 1 Neither direction favored; approx. equal parts of both react & pdts present 3.K eq >> 1 Forward rxn is favored; fwd rxn proceeds to almost completion; at equil. more pdts than reactants present

12. E RXN. PROCEEDS PCl 3 (g) + Cl 2 (g) -----  PCl 5 (g) PCl 3 +Cl 2 PCl 5 PCl 3 Cl - Cl - Intermediates Reactant breaking apart Intermediates Reactant formation of products

13. GIBBS ENERGY,  G -  G,  G < 0 spontaneous +  G,  G > 0 reverse spont  G = 0 equilibrium  G & EQUILIBRIUM  G o < 0, forward rxn proceeds &  G increase till equil reached  G o > 0, reverse rxn proceeds &  G decrease till equil reached

14. H 2 (g) +.5 O 2 (g) ---> H 2 O (l) + 258.8 kJ 40.7 kJ + H 2 O (l) ---> H 2 O (g) Look at the 2 rxns. listed below Interrupt each rxn. Think, what does it say about  H? Write rxn w/o kJ, show  H Original written rxn, think in terms of E & what is happening  H = -258.8 kJ  H = +40.7 kJ