Short Answer
Latent heat of vaporization is the amount of heat energy required to change a liquid into a gas at its boiling point without changing its temperature. During this process, the liquid absorbs heat, but its temperature remains constant until the entire liquid is converted into vapor. This heat is used to overcome the forces of attraction between liquid particles.
For example, when water boils at 100°C, it absorbs latent heat of vaporization to turn into steam. The temperature stays at 100°C until all the water becomes gas.
Detailed Explanation :
Latent Heat of Vaporization
Latent heat of vaporization is the special amount of heat energy needed to convert a liquid into a gas at its boiling point without any rise in temperature. The term “vaporization” means changing a liquid into vapor. When a liquid is heated, its particles move faster due to the absorption of heat. At the boiling point, particles gain enough energy to completely break free from the forces holding them together. The energy needed for this change of state—without increasing temperature—is called the latent heat of vaporization.
This concept is very important for understanding boiling, evaporation, cloud formation, cooling, and many everyday activities involving liquids and gases.
How Latent Heat of Vaporization Works
Latent heat of vaporization comes into action when a liquid reaches its boiling point.
- Heating the Liquid
When a liquid is heated:
- The particles absorb heat energy
- They move faster
- Temperature rises gradually
This continues until the liquid reaches its boiling point.
- At the Boiling Point
At the boiling point:
- The liquid starts converting into gas
- Vapor bubbles form inside the liquid
- Heat continues to be absorbed but temperature remains constant
The thermometer remains steady even though heating is going on.
- Breaking the Forces of Attraction
Liquids have moderate intermolecular forces that keep particles close.
To change into gas, particles must completely break these forces.
The heat supplied during vaporization is used to:
- Separate particles from each other
- Allow them to move freely as gas
- Increase the particles’ distance
Since the heat does not increase temperature, it is called latent (hidden) heat.
- Complete Vaporization
Once all liquid has turned into gas:
- Particles are far apart
- They move freely in all directions
- Temperature will rise again if heating continues
Until then, the temperature stays constant.
Importance of Latent Heat of Vaporization
Latent heat of vaporization is involved in many natural and daily-life processes.
- Cooling Effect of Evaporation
Evaporation uses latent heat of vaporization from the surroundings.
Examples:
- Sweat evaporates and cools the body
- Water in clay pots stays cool
- Alcohol feels cool on the skin
This happens because evaporation absorbs heat from the surface.
- Cloud Formation and Rain
- Water from oceans evaporates using latent heat
- Vapor rises and cools
- Latent heat is released during condensation
- Clouds form and later rainfall occurs
This cycle depends greatly on latent heat of vaporization.
- Boiling and Cooking
When water boils:
- It uses latent heat to turn into steam
- The temperature stays at 100°C
- Steam carries a huge amount of latent heat
This is why steam burns are more severe than hot water burns.
- Refrigeration and Air Conditioning
These systems rely on vaporization and condensation.
During vaporization:
- The liquid coolant evaporates
- It absorbs latent heat from the surroundings
- The surroundings become cool
This is how refrigerators and ACs cool air.
Examples of Latent Heat of Vaporization
Different liquids require different amounts of energy to vaporize.
- Water has a high latent heat of vaporization
- Alcohol has a lower latent heat
- Ether vaporizes very easily
The stronger the forces of attraction in a liquid, the higher the latent heat.
Why Temperature Remains Constant During Vaporization
During vaporization:
- Heat energy is not used to raise temperature
- Instead, it is used to separate particles
- This energy becomes “hidden,” so temperature stays steady
Only after the liquid fully turns into vapor does the temperature rise again.
Latent Heat During Condensation
During condensation (gas → liquid), latent heat of vaporization is released.
Example:
- Steam condensing on skin releases heat
- This makes steam burns very painful
The reverse process releases the same amount of heat absorbed during vaporization.
Conclusion
Latent heat of vaporization is the heat energy required to convert a liquid into a gas at its boiling point without changing its temperature. This energy helps particles break free from each other and form vapor. It plays an important role in boiling, cooling, weather formation, and many scientific and everyday processes. Understanding this concept helps explain how liquids behave when heated and how energy is involved in state changes.