Absorption and Adsorption

Absorption and adsorption are two very important concepts in chemistry, physics, and environmental science. Students often get confused between these two because the words look similar but their meanings are completely different. This article explains both terms in a clear, simple, and pointwise manner with definitions, examples, diagrams (conceptual explanation), applications, FAQs, and revision notes.

What is Absorption?

Absorption is a surface-independent process in which a substance enters and spreads uniformly throughout another substance.

Key Points About Absorption

In absorption, the particles enter inside the material.
It is a bulk phenomenon because it happens throughout the body of the absorber.
The absorbed substance becomes part of the entire volume.
Example: Water absorbed by a sponge.
Example: Carbon dioxide absorbed in water (forms carbonic acid).
Example: Human digestive system absorbs nutrients inside the intestine.

Important Facts

Absorption depends on the temperature, pressure, and nature of both the absorbing and absorbed substances.
Rate of absorption is usually slower because the molecules penetrate deep into the material.
Absorption is common in solids, liquids, and biological systems.

What is Adsorption?

Adsorption is a surface phenomenon in which molecules stick to the surface of a solid or liquid.

Key Points About Adsorption

Only the surface is involved.
Adsorption is a surface phenomenon.
The substance that sticks is called adsorbate.
The surface on which it sticks is called adsorbent.
Example: Charcoal trapping gases on its surface.
Example: Silica gel adsorbing moisture.
Example: Dust particles sticking on walls or skin.

Important Facts

Adsorption happens very fast compared to absorption.
Adsorption can be physical (weak forces) or chemical (strong forces).
Adsorption increases with high surface area (e.g., powder, porous materials).

Difference Between Absorption and Adsorption

This is one of the most searched questions online: absorption vs adsorption difference.

1. Definition

Absorption: Substance enters inside another.
Adsorption: Substance sticks to surface.

2. Type of Phenomenon

Absorption: Bulk phenomenon.
Adsorption: Surface phenomenon.

3. Speed

Absorption: Slow.
Adsorption: Fast.

4. Concentration

Absorption: Uniform throughout.
Adsorption: Highest at the surface.

5. Temperature Effect

Absorption: Increases with temperature (mostly).
Adsorption: Decreases with increase in temperature (exothermic).

6. Practical Examples

Absorption: Sponge absorbing water.
Adsorption: Activated charcoal removing impurities.

7. Industrial Use

Absorption: Refrigeration, chemical storage.
Adsorption: Water purification, gas masks, air filters.

What are the Types of Absorption?

1. Physical Absorption

No chemical reaction occurs.
Example: Hydrogen dissolved in palladium.

2. Chemical Absorption

Chemical reaction occurs between absorbent and absorbate.
Example: CO₂ absorbed in alkalis.

3. Biological Absorption

Happens in plants and animals.
Example: Nutrient absorption in intestines; water absorbed by plant roots.

What are the Types of Adsorption?

1. Physical Adsorption (Physisorption)

Weak van der Waals forces.
Low heat of adsorption.
Reversible process.
Occurs more at low temperatures.

2. Chemical Adsorption (Chemisorption)

Strong chemical bonds.
High heat of adsorption.
Irreversible.
Requires high temperature.

What is Sorption?

Many students search “What is sorption in chemistry?”
Sorption is a combined process of absorption and adsorption.

Key Points

Sorption = Absorption + Adsorption
Used in environmental science and chemical engineering.

What is Desorption?

Desorption is the opposite of adsorption.

Key Points

It is the process in which adsorbed molecules leave the surface.
Happens when temperature increases or pressure decreases.
Used in purification and regeneration of filters.

What is Absorbent and Adsorbent?

Absorbent

Material that allows particles to enter inside it.
Examples: Sponge, cotton, soil, liquids.

Adsorbent

Material with high surface area for sticking particles.
Examples: Activated charcoal, silica gel, zeolites, clay.

Factors Affecting Absorption

1. Temperature

Higher temperature increases absorption in most cases.

2. Pressure

More pressure equals more absorption of gases in liquids.

3. Nature of Materials

Polar substances absorb polar substances easily.

4. Surface Area

More surface area increases rate of absorption.

5. Concentration

Higher concentration leads to faster absorption.

Factors Affecting Adsorption

1. Surface Area

Higher surface area equals more adsorption.
Powdered charcoal adsorbs more than a charcoal block.

2. Temperature

Adsorption decreases with high temperature.

3. Pressure

Higher pressure increases adsorption of gases.

4. Nature of Adsorbent

Porous materials adsorb best.

5. Nature of Adsorbate

Easily liquefiable gases adsorb more.

Real-Life Examples of Absorption

Sponge soaking water
Soil absorbing rainwater
Food nutrients absorbed in the intestine
Ink absorbed by blotting paper
Water absorbed by paper towels
Oxygen absorbed by blood

Real-Life Examples of Adsorption

Activated charcoal in water purifiers
Silica gel in shoe boxes adsorbing moisture
Gas masks using charcoal to adsorb toxic gases
Colored substances sticking to clothes in dyeing
Smoke adsorbed by chimney filters
Odor molecules adsorbed by deodorants

Applications of Absorption

1. Industrial Applications

Gas absorption in chemical plants
Ammonia absorption in refrigeration
Liquid fuel absorption systems
Absorption towers in fertilizers and cement industries

2. Biological Applications

Nutrient absorption in digestion
Oxygen absorption by blood
Mineral absorption in plants

3. Environmental Applications

Soil absorbing pollutants
Plants absorbing CO₂
Water bodies absorbing heat energy

Applications of Adsorption

1. Water Purification

Activated charcoal removes impurities and bad smell.

2. Air Purification

Gas masks
Air purifiers
Smoke absorption filters

3. Industrial Applications

Adsorption chromatography
Catalysis (solid catalysts work by adsorption)
Drying agents (silica gel, alumina)

4. Environmental Applications

Removing pollutants from water
Removing toxic gases from factories
Controlling odor and smoke

5. Daily Life

Toothpaste polishing teeth
Activated carbon in beauty products
Refrigerator deodorizer
Dye adsorption in clothes

Frequently Asked Questions (FAQs)

1. What is the simple definition of absorption?

Absorption is a process in which one substance completely enters and mixes into another.

2. What is the simple definition of adsorption?

Adsorption is a process where particles stick only to the surface of a material.

3. What is the main difference between absorption and adsorption?

Absorption is a bulk phenomenon; adsorption is a surface phenomenon.

4. Which is faster — absorption or adsorption?

Adsorption is faster than absorption.

5. What is the example of absorption?

Sponge absorbing water.

6. What is the example of adsorption?

Charcoal adsorbing impurities.

7. Is adsorption reversible?

Physical adsorption is reversible; chemical adsorption is usually irreversible.

8. What is sorption?

Sorption is a combination of absorption and adsorption.

9. What is desorption?

Desorption is the release of substances previously adsorbed on a surface.

10. Why is activated charcoal used in filters?

Because it has a very large surface area for adsorption.

11. Which process is used in digestion — absorption or adsorption?

Absorption.

12. Which process removes bad odors?

Adsorption by activated carbon or deodorizing agents.

Conclusion

Absorption and adsorption are two essential concepts in chemistry with huge importance in daily life, industry, biology, and environmental science. Absorption involves penetration into the bulk, while adsorption is restricted to the surface. Understanding the differences between them helps students score better in exams, understand scientific phenomena clearly, and connect science with real-world applications like water purification, air filtration, digestion, refrigeration, and pollution control.

Both processes—though similar in spelling—have completely different mechanisms and uses. Mastering these concepts makes your foundation stronger for Class 9, Class 10, Class 11 Chemistry, NEET, JEE, and board exams.