Give one example of each.
5.1 Distinguish between the meaning of the terms ausorption and absorption
5.2 What is the difference between physisorption and chemisorption?
Answers
Answer:
answer of 5.1-
Distinguish between the meaning of the terms adsorption and absorption. Give one example of each. Adsorption is a surface phenomenon of accumulation of molecules of a substance at the surface rather than in the bulk of a solid or liquid. ... On the other hand, the process of absorption is a bulk phenomenon.
Explanation:
answer of 5.2-
Depending on the substance being deposited and adsorbed, adsorption is classified into two types:
Physisorption
Chemisorption
Physisorption
Physisorption is also known as physical adsorption and it is an exothermic process. Its adsorption enthalpy is low, nearly 20 to 40 kJ/mol. Normally in physisorption, the gas is accumulated on the solid surface due to weak force, known as Van der Waals forces.
Physisorption lacks specificity because of the adsorbent (the surface or the material on which the process of adsorption takes place) in the given surface does not show any particular gas. It has reversible nature that is physisorption of gas by a solid can be reversed to a solid by gas.
Gas + solid = Solid/Gas + Heat
An example of physisorption is the adsorption of gases like hydrogen, nitrogen etc at lower temperature on the surface of adsorbent like charcoal.
Physisorption depends on the surface area of the adsorbent. As surface area increases, the extent of adsorption also increases. For example, finely divided metals and porous substances have a large surface area. So that they are considered as good adsorbents. It also depends on the nature of the adsorbate (the accumulation of molecular species or substance at the surface).
Chemisorption
Chemisorption is also known as chemical adsorption. In chemisorption, adsorption takes place in adsorbed substance that is held by chemical bonds. Chemisorption has high specificity that is it is highly specific, and it takes place only if there is a chemical bonding between adsorbent and adsorbate.
Chemisorption has irreversible nature and it also favours high pressure. Due to chemical bonding, enthalpy of adsorption of chemisorption is high nearly 80 to 240 kJ/mol. Physisorption of gas adsorbed at a lower temperature may be converted into chemisorption at a higher temperature.
Chemisorption depends on the surface area. As the surface area of the adsorbent increases, chemisorption also increases. An example of chemisorption is the adsorption of hydrogen, nitrogen etc on the surface of adsorbent like ferrous catalyst at a high temperature.
Difference Between Physisorption And Chemisorption
Physisorption Chemisorption
It is due to the formation of van der Waals forces. It is due to the formation of chemical bonds.
It is reversible in nature. It is irreversible in nature.
Physisorption is not specific in nature. It is very specific in nature.
It has low adsorption enthalpy nearly 20 to 40 kJ/mol. Chemisorption has high adsorption enthalpy nearly 80 to 240 kJ/mol.
It favours low temperature. It favours high temperature.
Physisorption decreases with increase in temperature. Chemisorption increases with increase in temperature.
It results in a multimolecular layer. It results in a unimolecular layer.
Activation energy is less in physisorption. Activation energy is high in chemisorption
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Answer:
1. During adsorption, the concentration of one substance on the surface of other substance is much higher than the concentration in the bulk. On the other hand, during absorption, there is uniform distribution of molecules of one substance throughout the body of other substance.
Thus, silica gel adsorbs water vapour while anhydrous calcium chloride absorbs water.
2. Physisorption Chemisorption
It is due to the formation of van der Waals forces. It is due to the formation of chemical bonds.
It is reversible in nature. It is irreversible in nature.
Physisorption is not specific in nature. It is very specific in nature.
It has low adsorption enthalpy nearly 20 to 40 kJ/mol. Chemisorption has high adsorption enthalpy nearly 80 to 240 kJ/mol.
It favours low temperature. It favours high temperature.
Physisorption decreases with increase in temperature. Chemisorption increases with increase in temperature.
It results in a multimolecular layer. It results in a unimolecular layer.
Activation energy is less in physisorption. Activation energy is high in chemisorption.
Explanation:
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