Short Answer

The change of state in matter is affected mainly by two factors: temperature and pressure. When temperature increases, particles gain energy and move faster, causing solids to melt and liquids to evaporate. When temperature decreases, particles lose energy, causing gases to condense and liquids to freeze. Pressure also affects the state of matter by pushing particles closer together or allowing them to spread apart.

These factors control how and when matter changes from solid to liquid, liquid to gas, gas to solid, and other state changes. Different substances change state at different conditions depending on their particle arrangement and intermolecular forces.

Detailed Explanation :

Factors Affecting the Change of State

The change of state is the process in which matter changes from one form—solid, liquid, or gas—to another. This change happens because the particles in matter gain or lose energy, which affects how they move and how strongly they attract each other. Two major factors control state changes: temperature and pressure. These factors determine when a substance will melt, freeze, evaporate, boil, condense, sublimate, or undergo deposition.

Understanding these factors helps explain many natural and everyday processes, such as ice melting, water boiling, frost forming, and liquids evaporating.

1. Temperature

Temperature is the most important factor affecting the change of state. It controls the amount of energy that particles have.

1. Increase in Temperature

When temperature increases, heat energy is supplied to the particles. This causes particles to:

• Move faster
• Vibrate more strongly
• Spread apart
• Overcome intermolecular forces

This leads to the following changes:

Melting (Solid → Liquid)

When a solid is heated, its particles gain energy and break free from their fixed positions. The solid melts into a liquid at a specific temperature called the melting point.

Example: Ice melts into water at 0°C.

Evaporation and Boiling (Liquid → Gas)

With more heat, liquid particles move fast enough to escape into the air. Evaporation happens at any temperature, while boiling happens at a fixed temperature called the boiling point.

Example: Water boils at 100°C to form steam.

Sublimation (Solid → Gas)

Some solids, when heated, change directly into gas without becoming liquid.

Example: Camphor and dry ice undergo sublimation.

1. Decrease in Temperature

When temperature decreases, heat energy is removed from the particles. This causes particles to:

• Slow down
• Move closer
• Strengthen intermolecular attraction

This leads to the following changes:

Freezing (Liquid → Solid)

Cooling a liquid reduces its particle movement, causing it to freeze into a solid at a specific temperature called the freezing point.

Example: Water freezes into ice at 0°C.

Condensation (Gas → Liquid)

When gas particles lose energy, they come closer and form a liquid.

Example: Steam condenses to water droplets.

Deposition (Gas → Solid)

Some gases directly turn into solids when cooled strongly.

Example: Frost formation on leaves.

2. Pressure

Pressure also affects the change of state, especially for gases.

1. Increase in Pressure

When pressure increases, particles are forced closer together. This can change the state of matter by increasing intermolecular attraction.

Effects:

• Gas can change into a liquid when compressed.
• Liquids can become solids under very high pressure.

Example:
LPG (cooking gas) is stored as a liquid in cylinders because high pressure compresses it.

1. Decrease in Pressure

When pressure decreases, particles spread apart because there is more space for movement.

Effects:

• Liquids may boil at lower temperatures.
• Solids or liquids may turn into gas more easily.
• Gas can expand freely.

Example:
At high altitudes, water boils at less than 100°C because of low air pressure.

3. Nature of the Substance (Optional Supporting Factor)

Although temperature and pressure are the main factors, the nature of the substance also plays a role.

Factors within the substance include:

• Strength of intermolecular forces
  Strong forces result in higher melting and boiling points.
• Type of particles (atoms, ions, molecules)
  Ionic solids melt at very high temperatures because of strong bonds.
• Purity of substance
  Impurities lower melting points and raise boiling points.

Example:
Salt lowers the melting point of ice.

Important State Changes Affected by These Factors

• Melting
• Freezing
• Boiling
• Evaporation
• Condensation
• Sublimation
• Deposition

Each of these changes depends on how much energy particles have and how close or far apart they are.

Conclusion

The change of state in matter is mainly affected by temperature and pressure. Increasing temperature gives particles more energy, causing solids to melt and liquids to evaporate. Decreasing temperature removes energy, causing liquids to freeze and gases to condense or deposit. Increasing pressure forces particles closer, while decreasing pressure lets them spread apart. These factors explain how matter changes between solid, liquid, and gas forms in both natural and everyday situations.