**Gas**

**Definition:** Gas is one of the three fundamental states of matter, along with solid and liquid. It is characterized by having no definite shape or volume. Instead, gases take on the shape and volume of their container.

**Particle Arrangement:**
- Gas particles are widely spaced and move freely in all directions.
- They are not held together by strong forces of attraction and are in constant random motion.

**Interparticle Forces:**
- Gas particles have weak intermolecular forces of attraction.
- These forces allow the particles to move independently of each other.

**Expansion:**
- Gases have the ability to expand and fill any given space.
- When heated, gas particles gain kinetic energy and move faster, causing the gas to expand.

**Compressibility:**
- Gases are highly compressible, meaning they can be squeezed into a smaller volume.
- When pressure is applied to a gas, the particles can be brought closer together, reducing the volume occupied by the gas.

**Examples of Gases:**
- Oxygen, nitrogen, carbon dioxide, helium, hydrogen, etc.

**Applications:**
- Gases have various practical applications, such as in cooking (natural gas), heating (propane), and transportation (gasoline).
- Gases are also used in industries for manufacturing, refrigeration, and as fuel sources.

**Vapour**

**Definition:** Vapour refers to the gas phase of a substance that is normally a liquid or solid at room temperature and atmospheric pressure. When a liquid or solid undergoes evaporation or sublimation, the resulting gas is referred to as vapour.

**Particle Arrangement:**
- Vapour particles are similar to gas particles, as they are widely spaced and move freely.
- However, vapour particles are specifically derived from the evaporation or sublimation of a liquid or solid.

**Interparticle Forces:**
- Vapour particles also have weak intermolecular forces like gas particles.
- These forces allow the vapour particles to move independently, similar to gas particles.

**Formation:**
- Vapour is formed when a liquid evaporates or when a solid sublimes.
- The process of evaporation involves the liquid particles gaining enough kinetic energy to overcome intermolecular forces and escape into the gas phase.
- Sublimation occurs when a solid directly changes into a gas without going through the liquid phase.

**Examples of Vapour:**
- Water vapour, steam, alcohol vapour, etc.

**Applications:**
- Vapour has various applications, such as in steam engines, steam turbines, and steam power plants for generating electricity.
- Vapour is also utilized in industrial processes, such as drying, sterilization, and distillation.
- In everyday life, vapour plays a role in weather phenomena, such as cloud formation and precipitation.