Have you ever wondered what the real difference between steam and vapour is?
We often use both words interchangeably, especially when we see something hot and misty rising from boiling water. But scientifically, steam and vapour are not the same.
In this article, we’ll clearly explain what is steam, what is vapour, their differences, examples, and how each is formed, along with a simple comparison table.
🌫️ What Is Steam?
Steam is the gaseous form of water produced when water boils at 100°C (at normal atmospheric pressure).
When you boil water in a kettle or on the stove, the white mist you see rising is not pure steam—it’s a mixture of water vapour and tiny condensed droplets.
The pure steam (also called dry steam) is invisible and extremely hot.
🔹 Scientific Definition
Steam is the gaseous phase of water, formed by boiling or evaporation of liquid water, usually at 100°C and 1 atm pressure.
🔹 Types of Steam
- Wet Steam: Contains water vapour and small liquid droplets (visible).
- Dry Steam: Pure water vapour with no liquid content (invisible).
- Superheated Steam: Heated beyond the boiling point without condensation.
🔹 Examples
- Steam from a boiling kettle
- Steam engines and turbines
- Steam sterilizers and irons
🌬️ What Is Vapour?
Vapour is a general term for the gaseous form of any substance that is normally a liquid or solid at room temperature.
For example:
- Alcohol can turn into alcohol vapour,
- Iodine turns into iodine vapour,
- Camphor produces camphor vapour.
🔹 Scientific Definition
Vapour is the gaseous state of a substance that exists as a liquid or solid under normal temperature and pressure conditions.
🔹 Formation of Vapour
Vapour forms through:
- Evaporation (slow surface process below boiling point)
- Sublimation (solid changing directly to gas, e.g., camphor, iodine)
🔹 Examples
- Water vapour in the air
- Alcohol vapour from sanitizer
- Perfume vapour in the atmosphere
- Iodine vapour (purple gas)
⚖️ Steam vs Vapour – Key Differences
Here’s a clear, easy-to-understand comparison:
| Feature | Steam | Vapour |
|---|---|---|
| Definition | Gaseous form of water | Gaseous form of any liquid or solid |
| Formation | By boiling water (100°C) | By evaporation or sublimation |
| Temperature | High (≥100°C at 1 atm) | Can be below boiling point |
| Substance | Only water | Any substance |
| Visibility | May be visible when condensed | Usually invisible |
| Energy Content | High (used for mechanical power) | Usually low |
| Examples | Steam from kettle, steam engines | Alcohol vapour, iodine vapour |
🔬 Scientific Explanation
When water is heated, its molecules gain kinetic energy.
At 100°C, the energy becomes high enough for molecules to break free from liquid bonds, forming steam (water vapour).
However, other substances like alcohol or iodine can change into vapour even at room temperature because their intermolecular forces are weaker and require less energy to escape into the gaseous phase.
💡 Interesting Facts
- Pure steam is invisible — the white cloud you see is condensed water droplets.
- Vapour can exist even below boiling point, while steam requires boiling.
- Steam engines use high-pressure steam to produce motion energy.
- Water vapour is a greenhouse gas that helps regulate Earth’s temperature.
⚙️ Applications of Steam and Vapour
| Steam | Vapour |
|---|---|
| Power generation (steam turbines) | Perfume, alcohol, or chemical vapours |
| Cooking (pressure cookers, steamers) | Industrial drying and distillation |
| Sterilization in hospitals | Air fresheners and fragrances |
| Heating systems | Sublimation and evaporation studies |
❓ FAQs – Steam vs Vapour
1. Is steam the same as water vapour?
Not exactly. Water vapour is pure gaseous water, while steam often refers to a mixture of vapour and liquid droplets.
2. Can we see steam?
Pure steam is invisible. The visible “steam” you see is actually condensed water droplets.
3. Is vapour always hot?
No. Vapour can exist even at room temperature, like alcohol vapour.
4. Which has more energy – steam or vapour?
Steam (especially superheated steam) has more energy and is used for industrial work.
5. Is fog or cloud a vapour?
No. Fog and clouds are tiny liquid water droplets, not vapour.
🧭 Conclusion
To summarize:
All steam is vapour, but not all vapour is steam.
Steam specifically refers to water in its gaseous state, while vapour can refer to any substance that changes into a gaseous form under suitable conditions.
Understanding the difference between steam and vapour helps us in many fields—from science and engineering to everyday life.
The Bachchantop 
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