Water is a magical substance. It’s everywhere – in rivers, rain, plants, and even our own bodies. But have you ever thought about how water sticks together or climbs up plants from the roots?
It all happens because of two important properties of water:
👉 Cohesion
👉 Adhesion
Let’s understand these two in a simple way so you never get confused again — especially in your competitive exams!
✅ Explore all “Difference Between” topics in Chemistry
What is Cohesion?
Cohesion means that water molecules stick to each other.
Explanation:
Water molecules are like best friends – they love to stay together. This is because of something called hydrogen bonding.
Key Points:
- Cohesion = Same molecules attract each other
- It is due to hydrogen bonds
- Helps in droplet formation
- Makes water have high surface tension
Simple Example:
- When you drop water on a table, it forms round droplets – not because it’s lazy, but because the water molecules pull each other tightly.
What is Adhesion?
Adhesion means that water molecules stick to other substances.
Explanation:
Water is also friendly with other materials like glass, paper, or soil. So it sticks to them. This property is called adhesion.
Key Points:
- Adhesion = Different molecules attract each other
- It helps water spread or climb up surfaces
- Very useful in plants and daily life
Simple Example:
- Water climbing up a paper towel or spreading on a glass window – that’s adhesion in action!
Difference Between Cohesion and Adhesion in Water Molecules
| Feature | Cohesion | Adhesion |
|---|---|---|
| Definition | Attraction between similar molecules, e.g., water to water | Attraction between different molecules, e.g., water to glass |
| Intermolecular Force Type | Caused by hydrogen bonding among water molecules | Caused by intermolecular attraction between water and other substances |
| Key Example | Water droplets form due to mutual attraction | Water spreading on glass or climbing up a paper towel |
| Visible Effect | Formation of spherical droplets due to surface tension | Water clinging or spreading on other surfaces |
| Role in Capillary Action | Helps maintain a continuous column of water | Helps water climb surfaces like plant xylem walls |
| Surface Tension | Increases due to strong cohesive forces | Does not contribute significantly to surface tension |
| Biological Significance | Enables water to form droplets and resist external force | Aids in the transport of water in plants and other surfaces |
| Dependency | Depends on water-water interaction | Depends on the water-other material interaction |
| Measurement | Measured as part of surface tension | Measured via contact angle on a surface |
| Nature of Force | Inward pulling force among molecules | Outward attraction between molecules and the surface |
How These Help Plants Survive
- Plants use both cohesion and adhesion to move water from roots to leaves.
- This process is called capillary action.
- Water sticks to the plant vessels (adhesion) and also pulls other water molecules along (cohesion).
👉 This movement happens without any pump – all thanks to these two natural properties!
Memory Tip (Mnemonic)
Cohesion = “Cousins stick together” (same molecules)
Adhesion = “Ads stick to walls” (different molecules)
Sample Question
Q. Which property of water helps in forming droplets?
A. Adhesion
B. Cohesion
C. Evaporation
D. Osmosis
👉 Correct Answer: B. Cohesion
Summary in Simple Words
- Cohesion = Water sticks to itself
- Adhesion = Water sticks to other things
- Both are caused by attractive forces between molecules
- Both help in capillary action, crucial for plant survival
- Very important for science questions in competitive exams
Quick Revision Points
- Cohesion = Same | Adhesion = Different
- Cohesion → Surface Tension | Adhesion → Capillary Action
- Hydrogen bonding = Key to cohesion
- Adhesion makes water climb walls (like plant xylem)
