Can you please explain me the langmuir isotherm at low and high pressure what happens to the term aP/1+bP!and how those terms are neglected! Please elaborate it nicely and explain
Thanks and regards,
Vineet
Can you please explain me the langmuir isotherm at low and high pressure what happens to the term aP/1+bP!and how those terms are neglected! Please elaborate it nicely and explain
Thanks and regards,
Vineet
Langmuir Adsorption Isotherm Let us discuss about the Langmuir adsorption isotherm. The theoretical aspects based on the kinetic theory of gases, Langmuir derived an adsorption isotherm which is known as Langmuir adsorption isotherm. It is assumed that the adsorption sites are similar and independent of whether the neighboring sites are filled otherwise vacant. Next we see the explanation of Langmuir adsorption isotherm.
Explanation of Langmuir adsorption isotherm
- The adsorption of gaseous molecules on the surface of the solid adsorbent, it is called as the condensation.
- The desorption of gaseous molecules from the surface of the solid adsorbent, it is called as the evaporation.
Langmuir assumed that the dynamic equilibrium between the above two processes establishes or the rate of condensation and evaporation becomeequal. He also assumed that the adsorbate gas posses thickness of one molecule or unimolecular. Like that a fact is there in chemical adsorption, so Langmuir adsorption isotherm can be derived and represented in short as follows.
`(x)/(m)``=(ap)/(1+bp)`
Where a and b are constants and x/m and p are the terms similar to those expressed in freundlich isotherm. The above equation can be expressed in two situations.
- The first one is low pressures.
- The second one is called as the high pressures.
In the equation `(x)/(m)``=(ap)/(1+bp)`,if the pressure p is considered to be very low, the equation will be ofthe form x/m=ap because bp can be deserted in comparison to 1.
At high pressures, the equation `(x)/(m)``=(ap)/(1+bp)` will assume the form x/m= a/b because 1 can be neglected in comparison to bp. For determination of constants a and b the first equation can be inverted, as
`(x)/(m)``=(ap)/(1+bp)` `=(1)/(ap)` `+(b)/(a)``or(b)/(a)` `+(1)/(ap)`
Now, if a graph of m/x is plotted against 1/p, the value of the slope will be equal to 1/a and the intercept will be equal to b/a.
Hence, from these values, the values of constants a and b can be determined.
The freundlich adsorption isotherm if a graph of x/m against pressure (p) is plotted a curve as declare the following diagram.
This curve shows that at lower pressures the values of x/m increase with increase in the values of p but at high pressures, it remains almost constant even with the increase in pressure.
Let us discuss about the Langmuir adsorption isotherm. The theoretical aspects based on the kinetic theory of gases, Langmuir derived an adsorption isotherm which is known as Langmuir adsorption isotherm. It is assumed that the adsorption sites are similar and independent of whether the neighboring sites are filled otherwise vacant. Next we see the explanation of Langmuir adsorption isotherm.
Explanation of Langmuir adsorption isotherm
- The adsorption of gaseous molecules on the surface of the solid adsorbent, it is called as the condensation.
- The desorption of gaseous molecules from the surface of the solid adsorbent, it is called as the evaporation.
Langmuir assumed that the dynamic equilibrium between the above two processes establishes or the rate of condensation and evaporation becomeequal. He also assumed that the adsorbate gas posses thickness of one molecule or unimolecular. Like that a fact is there in chemical adsorption, so Langmuir adsorption isotherm can be derived and represented in short as follows.
`(x)/(m)``=(ap)/(1+bp)`
Where a and b are constants and x/m and p are the terms similar to those expressed in freundlich isotherm. The above equation can be expressed in two situations.
- The first one is low pressures.
- The second one is called as the high pressures.
In the equation `(x)/(m)``=(ap)/(1+bp)`,if the pressure p is considered to be very low, the equation will be ofthe form x/m=ap because bp can be deserted in comparison to 1.
At high pressures, the equation `(x)/(m)``=(ap)/(1+bp)` will assume the form x/m= a/b because 1 can be neglected in comparison to bp. For determination of constants a and b the first equation can be inverted, as
`(x)/(m)``=(ap)/(1+bp)` `=(1)/(ap)` `+(b)/(a)``or(b)/(a)` `+(1)/(ap)`
Now, if a graph of m/x is plotted against 1/p, the value of the slope will be equal to 1/a and the intercept will be equal to b/a.
Hence, from these values, the values of constants a and b can be determined.
The freundlich adsorption isotherm if a graph of x/m against pressure (p) is plotted a curve as declare the following diagram.
This curve shows that at lower pressures the values of x/m increase with increase in the values of p but at high pressures, it remains almost constant even with the increase in pressure.
