Comparison of Vapour and Gas with Examples
The Difference Between Vapour And Gas is a common question in physics and chemistry exams. Understanding this distinction is important for students in Classes 8–12 and for JEE/NEET aspirants, as it helps in mastering concepts related to states of matter and phase changes.
Definition of Vapour
Vapour refers to the gaseous state of a substance that is usually found as a liquid or solid at room temperature. Vapour is produced when a liquid or solid transitions into the gas phase upon heating, such as water turning into steam. For further reading, see Vaporization And Vapor Pressure.
Vapours can be easily condensed back to their liquid or solid form by cooling or by compressing the gaseous state. They exist in equilibrium with their condensed phase at a given temperature and pressure.
Definition of Gas
A gas is a substance that exists in the gaseous state under standard conditions of temperature and pressure. Typical gases such as oxygen or nitrogen do not have a liquid or solid phase under normal room conditions. Refer to the Difference Between Liquid And Gas for more details.
Gases do not have definite shape or volume and expand to fill any container. They can be liquefied only by applying high pressure and low temperature, and they rarely exist as solids or liquids at room temperature.
Difference Table
| Vapour | Gas |
|---|---|
| Gaseous state of a normally liquid/solid at room temperature | Exists as a gas at room temperature |
| Easily converts to liquid or solid on cooling | Requires high pressure and low temperature to liquefy |
| Can coexist in equilibrium with liquid or solid | Usually does not coexist with other phases at room temperature |
| Partial pressure is less than critical pressure | Pressure can exceed the critical value |
| Formed by evaporation or sublimation | Not formed by phase change at room temperature |
| Can be condensed by moderate compression | Requires very high compression to liquefy |
| Usually found near the liquid/solid phase boundary | Found far from liquid/solid boundary in phase diagram |
| Example: Water vapour | Example: Oxygen gas |
| Density is generally higher compared to gas | Density is generally lower at same conditions |
| Can quickly condense at room temperature | Remains in gaseous form at room temperature |
| Exhibits properties intermediate between liquid and gas | Exhibits true gaseous properties |
| May contain some liquid/solid particles in suspension | Pure form contains only gas molecules |
| Pressure and temperature near phase transition points | Pressure and temperature far from transition points |
| Common in natural processes like weather formation | Commonly used in industrial processes |
| Example: Camphor vapour by sublimation | Example: Helium gas in balloons |
| Forms clouds, mist, steam | Forms atmosphere, fuel gases |
| Term used for substances not normally gaseous | Term for substances primarily in gas form |
| Change to liquid/solid with small temperature drop | Stays gas unless temperature is drastically lowered |
| Less stable as gas at standard temperature | More stable as gas at standard temperature |
| Example in food: Steam used in cooking | Example in industry: Methane gas for heating |
Key Differences
- Vapour condenses easily at room temperature
- Gas exists in gaseous phase at normal conditions
- Vapour can coexist with liquid or solid phase
- Gases require extreme conditions to liquefy
- Vapour is formed by phase transition of solids/liquids
- Examples: water vapour versus nitrogen gas
Examples
Water vapour produced from boiling water is a classic example of vapour. Oxygen that is always present in the air is an example of a gas naturally found at room temperature. Related topics include Properties Of Gases And Vapours.
Applications
- Vapour used in steam engines and cloud formation
- Gases used in industrial fuels and refrigeration
- Vapour relevant in meteorological processes
- Gases used for respiration and combustion
- Vapour essential in chemical distillation techniques
- Gases important in Kinetic Theory Of Gases studies
One-Line Summary
In simple words, vapour is the gaseous form of substances usually found as liquids or solids at room temperature, whereas gas refers to substances that exist naturally in the gaseous state under standard conditions.
FAQs on What Is the Difference Between Vapour and Gas?
1. What is the difference between vapour and gas?
Vapour refers to the gaseous state of a substance that is normally a liquid or solid at room temperature, while gas refers to substances that exist in the gaseous state under standard conditions.
Key differences:
- Vapour can easily condense back into liquid or solid when cooled, but gas generally does not under normal conditions.
- Vapours are usually formed from substances with higher boiling points; gases naturally exist in the gaseous state above -273°C in nature.
- Examples of vapour: Steam (from boiling water), iodine vapour.
Examples of gas: Oxygen, Nitrogen, Hydrogen.
2. Can vapour be converted into gas?
A vapour can become a gas if heated sufficiently so it cannot easily revert to its liquid or solid phase under normal conditions.
This state change involves:
- Increasing temperature above the substance's critical temperature.
- Ensuring it cannot be condensed by normal pressure or cooling.
3. What are some examples of vapour and gas?
Some common examples of vapour and gas are:
- Vapour: Water vapour (steam), camphor vapour, iodine vapour, alcohol vapour.
- Gas: Oxygen (O2), hydrogen (H2), nitrogen (N2), carbon dioxide (CO2).
Vapours generally originate from substances that are liquid or solid at room temperature, unlike true gases.
4. Why is water vapour called vapour and not gas?
Water in the form of vapour is called vapour because water exists as a liquid at room temperature, so its gaseous form (steam) is considered a vapour.
- Vapour easily condenses into liquid (water) at room temperature.
- True gases like N2 or O2 do not condense under normal atmospheric conditions.
5. How does the compressibility of vapour and gas differ?
Both vapour and gas are compressible, but vapours are typically closer to their liquefaction point so they can be compressed and condensed more readily.
- Vapours condense easily when pressure is applied or temperature is lowered.
- Gases generally require much higher pressure or lower temperatures to liquefy.
6. Can you give a table comparing vapour and gas?
Here is a comparison between vapour and gas:
- Vapour:
- Substance is liquid or solid at room temperature.
- Easily condensed by cooling or compression.
- Gas:
- Substance is gaseous at room temperature.
- Difficult to condense under normal conditions.
7. What is the critical temperature and how does it relate to vapour and gas?
The critical temperature of a substance is the highest temperature at which it can be liquefied by pressure alone.
- Below the critical temperature, a substance can exist as a vapour and can be liquefied.
- Above the critical temperature, the substance exists as a true gas and cannot be liquefied by pressure.
8. Are vapour and gas the same state of matter?
Both vapour and gas are forms of the gaseous state, but the term vapour is used for substances not normally gaseous at room temperature, while gas is used for those naturally in the gaseous phase.
- Both have no fixed shape or volume and are highly compressible.
- The main difference lies in their natural state under standard conditions.
9. Why do vapours condense faster than gases?
Vapours condense faster than true gases because they are already close to their condensation (liquefaction) point at room temperature.
- Lowering temperature or increasing pressure changes vapour to liquid quickly.
- Gases require more drastic changes in temperature or pressure for condensation.
10. Give one point of difference between vapour and gas for CBSE exams.
Vapour returns to liquid or solid on cooling at room temperature, but gas does not easily liquefy under these conditions.
- Example: Water vapour (vapour) vs oxygen (gas).
