Catalysts:
Catalyst is defined as a forgion substance that alters the velocity for a
chemical reaction without itself undergoing any permanent chemical
change and the phenomena is called catalysis.
1. Positive catalyst 2.negative catalyst
There is homogeneous catalysis and heterogeneous catalysis.
Diffusion : is the movement of atoms within a material . atoms
move in an orderly fashion to eliminate concentration differences
and
produce a homogeneous uniform composition.
Rate of diffusion ( Fick first law)
The rate of atoms diffusion in a material can be measured by the flux
which is defined as the number of atoms passing through a plane of
unit area.
The diffusion coefficient D is related to temperature of Arrhenius
equation:
The second law of Fick is
(
)
(
√
)
Diffusion in solid state : in pure solid material atoms move from one
lattice position to another this process known as self-diffusion and
can be detected by using radioactive tracers.there are mechanism
such as
1.vacancy diffusion
2.interstitial diffusion
3.other diffusion mechanisms.