choical Chemistry Reaction Kinetic Thermodynamic aspects E/RT a=k ea ktoI-n-ASO/R-AHO/RT kr=",( e (23.33) ea=Ah+nRt Gas-phase reaction (23.34) kT A=Acoyl-me"eASc R Gas-phase reaction (23.35)
6 Physical Chemistry Thermodynamic Aspects o n S R H RT r o c o c c e e h k T k 1 / / ( ) − − − = (23.33) E H nRT o a = + Gas-phase reaction (23.34) E RT r a A k e / o n n S R o c c e e h k T A 1 / ( ) − = Gas-phase reaction (23.35) Reaction Kinetics
Ch ical chemistr Reaction Kinetic Catalysis Catalyst: a substance that increases the rate of a reaction and can be recovered chemically unchanged at the end of the reaction A catalyst Lower the activation energy Avoiding the slow, rate-determining step of the uncatalysed reaction Results in a higher reaction rate at the same temperature Activation energies of catalysed reactions Reaction Catalyst E。/kJmo1 2H→H2+l2 None 184 Au 105 Pt 59 2NH3>N2+3H2 None 350 W 162
7 Physical Chemistry Catalysis Catalyst: a substance that increases the rate of a reaction and can be recovered chemically unchanged at the end of the reaction. A catalyst Lower the activation energy Avoiding the slow, rate-determining step of the uncatalysed reaction Results in a higher reaction rate at the same temperature Activation energies of catalysed reactions Reaction Catalyst Ea / kJmol-1 2 2 2 HI → H + I 2NH3 → N2 +3H2 None 184 Au 105 Pt 59 None 350 W 162 Reaction Kinetics
Ch ical chemistr Reaction Kinetico Catalvsis (a) participate the reaction E<E A+B catalyst(K AB E<E E A+K→AK AK+B→AB+K (b)Lower the activation energy (c)High selectivity Reaction coordinate Can t change the reaction direction and reaction equilibrium 1)If Ar Gm(,P)>0, the reaction can not proceed even with catalysts (2 )The catalysts cant change standard equilibrium constants A, Gm(T, P)=-RT In Ko (3) The catalysts change both forward and backward reaction rates
8 Physical Chemistry Catalysis (a) Participate the reaction Can’t change the reaction direction and reaction equilibrium E1 E2 { Ea E } Reaction coordinate E1<Ea E2<Ea A B AB catalyst(K) + ⎯⎯⎯⎯⎯→ A+K →AK AK+B→AB+K (b) Lower the activation energy (c) High selectivity (1) If , r Gm(T,P) 0 the reaction can not proceed even with catalysts (2) The catalysts can’t change standard equilibrium constants o r Gm(T, P) = −RT ln K (3) The catalysts change both forward and backward reaction rates Reaction Kinetics
Ch ical chemistr Reaction Kinetic Catalvsis Ethanol Conversion 25 types of products Cu 200-250 c)CH,CHO÷2 A2O3T2→C2H4+H2O 350-360°C Alo CHOH →(C,H,O+H,O 250°C Zno. CrO ->CH=CH-CH=Ch+ho+h 400-4500C Na >ChoH+ho
9 Physical Chemistry Catalysis Ethanol Conversion ( ) ⎯⎯→ + → = − = + + − → + → + − → + ............................................. ............................................. C H O H H O C H C H C H C H H O H 400 450 C ZnO C r O C H O H O 250 C Al O C H H O 350 360 C Al O 或 ThO C H CHO H 200 - 250 C C u C H O H 4 9 2 N a o 2 2 2 2 2 3 o 2 5 2 2 2 3 o 2 4 2 2 3 2 o 3 2 2 5 or 25 types of products Reaction Kinetics