文档介绍：Reaction ics (7)
Xuan Cheng
Xiamen University
Physical Chemistry
1
Physical Chemistry
Thermodynamic Aspects
plex Theory: structure of the plex (?)
The concepts: an equilibrium between the reactants and the plex
The activation process is expressed in terms of thermodynamic function
()
()
()
()
Reaction ics
2
Physical Chemistry
Thermodynamic Aspects
()
For the process
()
By analogy to (), define
()
In terms of concentration
Gibbs energy of activation
()
Thermodynamic version of the TST expression for the rate constant.
Rate constant
Reaction ics
3
Physical Chemistry
Thermodynamic Aspects
()
()
Entropy of activation
()
()
()
Enthalpy of activation
Gibbs energy of activation
Reaction ics
4
Physical Chemistry
Thermodynamic Aspects
()
()
()
()
()
Gas-phase reaction
()
Reaction ics
5
Physical Chemistry
Thermodynamic Aspects
()
()
Gas-phase reaction
()
Gas-phase reaction
Reaction ics
6
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
None
184
Au
105
Pt
59
None
350
W
162
Reaction ics
7
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
(b) Lower the activation energy
(c) High selectivity
(1) If ,
the reaction can not proceed even with catalysts
(2) The catalysts can’t change standard equilibrium constants
(3) The catalysts change both forward and backward reaction rates
Reaction ics
8
Physical Chemistry
Ca