Latent Heat of Fusion and Vaporization

Have you ever wondered why ice melts without getting hotter or how water boils but stays at 100°C? This happens because of something called latent heat. Latent heat is the hidden energy needed to change a substance from one state to another, like from solid to liquid or liquid to gas, without changing its temperature.

In this article, we will explain important ideas like the latent heat of fusion, latent heat of vaporization, and specific latent heat in a simple way. You will learn about the latent heat of fusion of water, the latent heat of vaporization of water, and why these concepts are so important in chemistry and in our daily life. We will also talk about sublimation — when solids turn directly into gases.

What is Latent Heat?

Latent heat is the amount of energy that a substance needs to change its state — like from solid to liquid or liquid to gas — without changing its temperature. Even though heat is added or removed, the temperature stays the same during the phase change.

There are two main types of latent heat:

• Latent heat of fusion (solid to liquid, or liquid to solid)
• Latent heat of vaporization (liquid to gas, or gas to liquid)

Latent heat plays a big role in daily life, from ice melting in a glass to water boiling in a pot.

Do Check: Acetaldehyde

What is Latent Heat of Fusion?

Latent heat of fusion is the amount of energy needed to change a solid into a liquid at its melting point without changing its temperature.

For example, when ice melts into water, it needs to absorb a lot of heat without getting any hotter than 0°C until all the ice has melted.

The latent heat of fusion formula is:

Q=m×L_f

Where:

• Q = Heat energy (in joules or calories)
• m = Mass of the substance (in kg or g)
• L_f = Specific latent heat of fusion (in J/kg or cal/g)

Do Check: Isomeris

Latent Heat of Fusion in Chemistry

In chemistry, latent heat of fusion is studied to understand how materials behave during melting and freezing. It helps explain why substances absorb energy during phase changes.

The specific latent heat of fusion means the amount of heat needed to melt 1 kilogram or 1 gram of a substance without changing temperature.

Latent Heat of Fusion of Water

• The latent heat of fusion of water is 333.55 kJ/kg.
• In calories, the latent heat of fusion of water is about 80 cal/g.
• For ice, the latent heat of fusion is also 80 calories per gram.

This high value explains why ice takes a long time to melt, helping to regulate Earth's climate.

Latent Heat of Vaporization

Latent heat of vaporization is the amount of heat needed to change a liquid into a gas at its boiling point, again without changing the temperature.

The latent heat of vaporization of water is very high:

• Latent heat of vaporization of water ≈ 2260 kJ/kg or 540 cal/g.

That’s why boiling water takes so much energy, even though it stays at 100°C until all of it evaporates.

The specific latent heat of vaporization tells how much energy is needed to vaporize a specific amount of a substance.

Do Check: Reactivity Series

Sublimation in Chemistry

Sublimation is when a substance changes directly from a solid to a gas without becoming a liquid first.

Common examples:

• Dry ice (solid carbon dioxide) sublimating into gas.
• Snow disappearing into water vapor without melting in cold conditions.

Sublimation also involves latent heat — the energy needed to break the bonds of the solid and jump directly into the gas phase.

Important Values of Latent Heat

Here’s a simple table for quick reference:

Why is Latent Heat Important?

• Keeps Earth's temperature stable: The oceans absorb and release heat, keeping the planet from overheating or freezing.
• Weather and climate: Melting ice absorbs heat, cooling the air. Evaporating water removes heat from the environment, impacting weather patterns.
• Daily life: Ice packs use the high latent heat of fusion to reduce swelling by absorbing body heat.

Conclusion

The latent heat of fusion and latent heat of vaporization are key ideas that explain how substances change states without a temperature rise. Water’s high latent heat values make it essential for life, weather, and climate. Whether it's ice melting in your drink or clouds forming in the sky, latent heat is working quietly all around us!