文档介绍：Reaction ics (1)
Xuan Cheng
Xiamen University
Physical Chemistry
1
Physical Chemistry
Reaction ics
For example
-
-
Thermodynamics: spontaneous reactions (possible to take place)
Thermodynamics: can’t answer (1) how to make them happen (2) how fast they will take place (3) the reaction mechanism
Reaction ics
2
Physical Chemistry
Reaction ics
T, P, catalyst
T, catalyst
Chemical ics:
Chemical ics
The study of the rates and mechanisms of chemical reactions
A reacting system is not in equilibrium
Reaction ics
3
Physical Chemistry
Rate of Reaction
Consider the homogeneous reaction (occurs entirely in one phase)
()
The rate of conversion J
()
At equilibrium, J = 0
Reaction ics
4
Physical Chemistry
Rate of Reaction
()
()*
At constant V
The rate of reaction r
mol dm-3 s-1
mol cm-3 s-1
Reaction ics
5
Physical Chemistry
Rate Laws
For many reactions
()*
k: rate constant (rate coefficient), k = f (T, P)
, , : order or partial order
++ + n : overall order
The expression for r as a function of concentrations at a fixed temperature is called the rate law.
Reaction ics
6
Physical Chemistry
Reaction Orders
Zero-order
First-order
Second-order
Third-order
Negative First-order
-order
No simple order
Reaction ics
7
Physical Chemistry
Rate Laws
Reaction
Rate Law
Reaction ics
8
Physical Chemistry
Reaction Mechanisms
()
intermediate
()
Step (a)
Step (b)
Step (c)
Elementary reaction
Reaction actually occurs
Reaction ics
9
Physical Chemistry
Measurement of Reaction Rates
Chemical Method
The concentration of a reactant or product as a function of time
Reaction vessels
At constant T
At intervals
Slows down or stop the reaction
Rapidly analyze positions of the mixture
Cooling the sample
removing a catalyst
Diluting the mixture
Adding a species
Reaction ics
10