lecture 15 - Turn on Camptasia Recording! ... 1 Which is...

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Unformatted text preview: Turn on Camptasia Recording! ... 1 Which is the rate determining step? 1. A--> B 2. A--> C 3. A--> E 4. B > 4 B--> C 5. B--> D 6. C--> D 7. C--> E ... 2 For this proven reaction mechanism, what will be the rate equation?--> CO + NO t Overall: ti + CO ? NO 2 2 Slow Fast NO2 + NO2 --> NO3 + NO NO3 + CO--> NO2 + CO2 A. Rate = k[NO2][CO] [ ][ ] B. Rate = k[CO2][NO] C. Rate = k[NO2]2 D. Rate = k[NO2] E. Rate = k[NO3][CO] ... 3 Chemical Equations Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al(s) + 3 O2(g) ---> 2 Al2O3(s) ---> The numbers in the front are called stoichiometric coefficients The letters (s), (g), and (l) are the physical states of compounds. ... 4 Chemical Equations Because the same atoms are present in a reaction at the beginning and at the end, the amount of matter in a system does not change. The Law of the Conservation of Matter 2HgO(s) ---> 2 Hg(liq) + O2(g) ---> 5 ... Chemical Equations Because of the principle of the an equation conservation of matter, must be balanced. balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788 ... 6 Balancing Equations ___ Al(s) + ___ Br2(liq) ---> ___ Al2Br6(s) ---> ... 7 Examples of Chemical Equilibria E ilib i Formation of stalactites and stalagmites CaCO3(s) + H2O(l) + CO2(g) O(l Ca2+(aq) + 2 HCO3-(aq) ... 8 ... 9 Equilibrium When a reaction is at equilibrium, the q , rate of the forward reaction equals the rate of the reverse reaction. There is no net observed change in the system. We use when a system is at equilibrium. ... 10 Properties of an Equilibrium Equilibrium systems are DYNAMIC (in constant motion) REVERSIBLE can be approached from either direction Pink to blue Co(H2O)6Cl2 ---> Co(H2O)4Cl2 + 2 H2O Blue to pink Co(H2O)4Cl2 + 2 H2O ---> Co(H2O)6Cl2 ... 11 THE EQUILIBRIUM CONSTANT For any type of chemical equilibrium of the type -the f ll i i a CONSTANT (at a given T) th following is ( t i -K is unitless Always product over reactant! If K is known, we can predict concentrations of products or reactants. If we measure concentrations, we can calculate K. ... 12 Writing Equilibrium Expressions Solids and pure liquids NEVER appear in equilibrium expressions. S(s) + O2(g) SO2(g) H2CO3(aq) + H2O(l) HCO3-(aq) + H3O+ Because the solid does not appreciably change concentration. ... Because water is 55 M. 13 The Reaction Quotient, Q In general, ALL reacting chemical systems are characterized by their REACTION QUOTIENT, Q. aA + bB cC + dD If Q = K, then system is at equilibrium. ... 14 Reaction Quotient & Equilibrium Constant ... 15 Reaction Quotient & Equilibrium Constant At any point in the reaction ... 16 Reaction Quotient & Equilibrium Constant Equilibrium achieved In the equilibrium region [HI]2 = 55.3 = K [H2 ][I2 ] K = equilibrium constant ... 17 What is the equilibrium expression? NH3(aq) + H2O(l) aq) A. K= [NH4+] [OH-] NH [NH3] [H2O] NH B. K= [NH4+] [OH-] NH [NH3] NH C. K= [NH3] [H2O] NH [NH4+][OH-] NH ... NH4+(aq) + OH-(aq) aq) aq) D. K= [NH3] NH [NH4+][OH-] NH 18 Determining K 2 NOCl(g) NOCl(g) 2 NO(g) + Cl2(g) Place 2.00 mol of NOCl is a 1.00 L flask. At equilibrium you find 0 66 mol/L of NO 0.66 NO. Calculate K. Solution Set of an "ICE" table of concentrations [NOCl] NOCl] [NO] [Cl2] Initial Change Equilibrium ... 19 The Meaning of K 1. Can tell if a reaction is product-favored or productreactantreactant-favored. For N2(g) + 3 H2(g) 2 NH3(g) Conc. of products is much greater than that of reactants at equilibrium. The reaction is strongly ___________favored. ... 20 The meaning of K AgCl(s) AgCl(s) Ag+(aq) + Cl-(aq) aq) aq) [Cl Kc = [Ag+] [Cl-] = 1.8 x 10-5 Conc. of products is much less than that of reactants at equilibrium. The reaction with small K is strongly ________________-favored. Ag+(aq) + Cl-(aq) AgCl(s) is product-favored. product- ... 21 ProductProduct- or Reactant Favored ProductProduct-favored K>1 ... ReactantReactant-favored K<1 22 Butane Isobutane ... 23 Product or reactant favored? ... 24 ...
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This note was uploaded on 04/15/2008 for the course CHEM 112 taught by Professor Hardy during the Spring '08 term at UMass (Amherst).

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