10 differences between Absorption and Adsorption

Last Updated on July 17, 2020 by Sagar Aryal

differences between Absorption and Adsorption (Absorption vs Adsorption)

Absorption Definition

Absorption, in biology, is the process of taking or assimilating substances into the cell or across the tissues by the process of diffusion or osmosis.

  • Absorption of substances into a cell or tissue usually occurs through the general surface of the cell.
  • The rate and process of absorption depend on a number of factors like the concentration of the substance, surface area and duration of contact, and solubility of the material.
  • The substance that is taken in is termed absorbate, whereas the substance that takes in the absorbate is terms absorbent.
  • Absorption takes place due to the presence of empty spaces within the molecules of the absorbent, which are then filled by the molecules of absorbate.
  • The process of absorption might occur either without the application of energy (diffusion) or with the expenditure of energy (active transport).
  • Absorption is an endothermic process where the heat energy of the system increases after taking in new molecules.
  • In most of the cases of absorption, solid substances dissolve in the liquid phase and then are absorbed into the cell or tissue.
  • Absorption is a bulk phenomenon where the absorbed material is uniformly distributed throughout the absorbent and thus affects the entire system.
  • Absorption occurs in all living and non-living systems either to intake nutrients or to maintain the homeostasis or concentration of substances across a surface.
  • The interactions between the absorbent and absorbate are physical and non-specific. Also, no chemical forces are involved.

Adsorption Definition

Adsorption is the process of adhesion of molecules of liquid or gases onto the surface of a solid particle.

  • This is the ability of solid particles/surfaces to attract the molecules of liquid and gas towards their surface after they come in contact with the molecules.
  • Adsorption is a surface phenomenon where the molecules form a layer of adsorbate around the adsorbent.
  • The process of adsorption occurs due to the surface energy where the attachment is facilitated either by Van der Wall’s force or by covalent bonds depending on the nature of the substances involved.
  • In physical adsorption molecules are attached to each other simply by Van der Wall force of attraction and no chemical specificity is present between the particles.
  • In chemical adsorption, however, bonds are formed between the adsorbate and the adsorbent and the bonds are specific for each adsorbate-adsorbent combination.
  • Adsorption is widely utilized in various separation techniques like adsorption chromatography and ion-exchange chromatography.
  • These processes allow the separation of molecules by selectively transferring the molecules of the liquid phase onto the surface of solid adsorbent.
  • Adsorption is also utilized by viruses where they attach to the surface of either bacteria or other organisms before penetration.
  • Adsorption is affected by a number of factors depending on the nature of the substances involved.
  • Some common factors include pressure, temperature, area of contact, and the nature of the interaction between the adsorbent and the adsorbate.
  • The process of adsorption is always exothermic as it leads to a decrease in the residual forces on the surface of the adsorbate.

Key differences (Absorption vs Adsorption)

Basis for comparison

Absorption

Adsorption

DefinitionAbsorption is the process of taking or assimilating substances into a surface like a cell or across the tissues by the process of diffusion or osmosis.Adsorption is the process of adhesion of molecules of liquid or gases onto the surface of a solid particle.
PhenomenonAbsorption is a bulk phenomenon where molecules of absorbate enter into the absorbent.Adsorption is a surface phenomenon where the molecules simply attach to the surface of the adsorbent.
PrincipleSubstances get absorbed into an absorbent due to the availability of space and the nature of the particle.Substances get adsorbed onto the surface of an adsorbent because the adsorbent has vacant spaces that stimulate the adhesion of particles onto the spaces.
Heat exchangeAbsorption is an endothermic process as the energy is given from the outside of the surface, and the overall energy of the absorbent increases after absorption.Adsorption is an exothermic process as the energy of the surface decreases as it leads to a reduction in residual forces of the surface.
RateAbsorption takes place at a uniform rate.The rate of adsorption increases steadily until it reaches equilibrium.
BondingThe absorbed materials remain in the absorbent without having any chemical interactions with the absorbent.The adsorbed materials remain attached to the adsorbent with either Van der Wall’s forces or covalent bonds.
TemperatureAbsorption doesn’t depend on the temperature of the system.Adsorption is a temperature-dependent phenomenon.
ConcentrationThe concentration of the absorbate in the absorbent is uniform after absorption.The adsorbate is more concentrated on the surface than the other parts of the adsorbent.
SeparationAbsorbed materials can be separated into different phases based on their chemical interaction with the phases.Adsorbed materials can be separated by passing new substance through the surface of the adsorbent, which replaces the previously adsorbed material.
ApplicationVarious living and non-living systems utilize absorption. Living systems like unicellular organisms use the absorption phenomenon for the intake of nutrients and water. Non-living systems like refrigerators utilize absorption for cold storage.Various living and non-living systems also utilize adsorption. Living systems like viruses use the phenomenon of adsorption for attachment to the bacteria or other organisms. Separation processes like adsorption chromatography use the principle of adsorption for the separation of mixtures.

Examples of Absorption

Skin absorption

  • Skin absorption is the process of taking in substances through the surface of skin either just into the skin or into circulation.
  • Skin absorption provides a route for the entry of chemicals into the body either as toxins or as medication.
  • The process of absorption in skin affected by a number of factors like the concentration of the substance, duration, and area of contact, the solubility of the chemicals, and the physical condition of the skin.
  • The absorption process in the skin is a passive process that doesn’t require the expenditure of energy.
  • The most crucial application of skin absorption is the dermal application of medicine which allows a localized action, unlike ingestion and injection.
  • However, the nature of skin to absorb things might also lead to skin diseases like dermatitis. Prolonged exposure to chemicals results in the absorption of larger volumes of chemicals that are harmful to the skin and the body.

Intestinal absorption

  • Absorption of nutrients and water into circulation is one of the important functions of the digestive system.
  • Absorption in the digestive system is an active process that takes place by the expenditure of energy.
  • The epithelium surface of the small and large intestine absorbs nutrients and water which are later passed into circulation.
  • Intestine, unlike skin, does a selective absorption of substances, ensuring the entry of only necessary and essential materials.

Absorption refrigerators

  • Absorption refrigerators are a special type of refrigeration system that utilizes the concept of absorption for the cooling of substances.
  • These refrigerators first evaporate the refrigerant liquid, which is then absorbed by another liquid to create a low partial pressure.
  • Finally, the refrigerant liquid is heated to evaporate the heat out of the refrigerator.
  • Absorption refrigerators are commonly used in recreational vehicles (RVs) and caravans as they can operate on propane fuel rather than electricity.

Examples of Adsorption

Adsorption of viruses

  • During viral infections, the first step in viral replication is the attachment and adsorption of the virus on the surface of the organism.
  • Adsorption of the virus is achieved when the specific proteins on the viral capsid bind to the receptors present on the surface of the organism.
  • These interactions are highly specific and play an essential role in viral replication.
  • The interactions are chemical bonds that are formed between different proteins.
  • Viral adsorption is affected by the pH change and temperature of the surface.

Adsorption chromatography

  • Adsorption chromatography is a separation technique that utilizes the principle of adsorption for the separation of various particles in a mixture.
  • Based on the affinity of the particles in the mixture to the stationary phase, bonds are formed, which helps in the separation of materials with higher affinity and lower affinity.
  • The particles of the mixture move through the stationary phase where the particles adsorb onto the vacant spaces on the stationary phase.
  • The molecules with lower affinity simply move through the system and are collected separately.
  • The interactions formed between the particles and the stationary phase is specific and are mostly chemical bonds.

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