3 ex. 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) (1) spontaneous process :it occurs without outside intervention.(2) spontaneous rxn & speed thermodynamics vs kineticsthe science of E transfer predict occurstudy of the rates of rxn why somes are fast or slow?vsex. 2Na(s) + 2H2O(l) NaOH(aq) + H2(g)Product favored ; reactant favored (spontaneous rxn)
5 (3) why product - favored ? DH < energy ? (exothermic)How about H2O(s) → H2O(l) DH > 0 at 0℃(4) something else ! Entropy ( S )S = the driving force for a spontaneous process is an increase in the entropy of the universe.= a measure of randomness or disorder of a system the great the randomness, the greater S.= the number of arrangements probability the higher probability, the higher S
7 ( S = 0 for a perfect crystal at 0 K) (6) DS = Sf - Si (5) S 0 H , E ?( S = 0 for a perfect crystal at 0 K)(6) DS = Sf - Si(7) generalization :a) S(g) >> S(l) > S(s)b) S : more complex molecules > simpler(ex) : CH3 CH2 CH3 > CH3 CH3 > CH4c) S : ionic solid (weaker force) > ionic solid (stronger force)(ex) : NaF(s) > MgO(s)d) liq and solid dissolve in a solvent DS > 0gas dissolve in a solvent DS < 0
9 In any spontaneous process, there is always an increase in the entropy of the universe DSuniv. > for spontaneous rxnDSuniv. = DSsys. + DSsurr.System: rxn R PDSuniv. > 0 rxn →DSuniv < 0 rxn ←DSuniv = 0 rxn at equilibrium
10 a) sign ( ＋ or －) depend on “heat flow” ex) H2O(l) ─→ H2O(g)(1) System(l) → (g) 18 ml (1 mol) → 31 LDSsys. > 0(2) Surroundinga) sign ( ＋ or －) depend on “heat flow”exothermic process DSsurr > 0endothermic process DSsurr < 0
11 b) magnitude depend on the temp. T 100 oC for rxn H2O(l) ─→ H2O(g)(3) DSuniv = DSsys + DSsurrconst. T & Pqp = | DH |
13 DG < 0 R → P spontaneou DG > 0 R ← P nonspontaneous G is a thermodynamic function that gives information about the spontaneity of the system.G = H - TS (for system)DG = DH - TDSsys (const. T & P)DG < R → P spontaneou DG > R ← P nonspontaneousDG = R P equilibrium
14 DG = DH - TDSsysDHo < 0DSo > 0DHo > 0DSo < 0at All temp.at High temp.spontaneousat Low temp.No Way !!Table
19 (3) free energy (G) (at const. T & P) spontaneousDG determines a rxn nonspontaneousequilibrium(4) S → absolute values DST1→T2S = 0 for a perfect crystal at 0 oK3rd law of thermodynamics(5) standard entropy So (298 K & 1 atm)
20 (1) DHo ： measured by calorimeter (2) DGo ： standard free energy change25 ℃ , 1 atm The more negative the value of DGo , the further a rxn will go to the right. Can be calculated by DGo = DHo - T DSoex. 17.9 DGorxn can be calculated by using Hess’s lawex
21 thermodynamically unstable rxn ← when high temp. DGorxn can be calculated using Hess’s lawkinetically stablethermodynamically unstablerxn ← when high temp.
22 DGof = standard free energy of formation DGof = 0 for elementsex & 17.12
25 (1) Slarge V > Ssmall V Slow P > Shigh P G = Go + RT ln(P) Go : the gas at the P = 1 atmG : the gas at the P = Pex. N2(g) + 3H2(g) → 2NH3(g)DG = Gproducts – Greactants= 2GNH3 – (GN2 + 3GH2)where GNH3 = GoNH3 + RT ln(PNH3)GN2 = ?GH2 = ?
26 (2) The meaning of DG for a chemical rxn. DG = (2GoNH3 – GoN2 – 3GoH2)+ RT [2ln(PNH3) – ln(PN2) – 3ln(PH2)]= DGo + RTln[(PNH3)2/ (PN2)(PH2)3]DG = DGo + RTlnQ(2) The meaning of DG for a chemical rxn.