Factors Affecting the States of Matter

1. Effect of Temperature

How Temperature Affects the State of Matter?

• Matter is made up of tiny particles (atoms/molecules) that are constantly moving.
• When temperature increases, the particles gain kinetic energy, move faster, and overcome the intermolecular forces holding them together.
• As a result, matter changes from one state to another (solid → liquid → gas).
• Example: Ice melts into water when heated because the heat energy increases molecular movement, weakening the forces keeping ice solid.

Detailed Process of State Change Due to Temperature:

(A) Solid to Liquid (Melting / Fusion)

• What happens?
  • When a solid is heated, its particles gain energy and vibrate faster.
  • At a certain temperature (melting point), the particles break free from their fixed positions and turn into a liquid.
• Example: Ice melts at 0°C to form water.

(B) Liquid to Gas (Boiling / Vaporization)

• What happens?
  • When a liquid is heated, its particles move even faster and overcome the attraction between them.
  • At a specific temperature (boiling point), the liquid changes into a gas.
• Example: Water boils at 100°C to form steam.

(C) Gas to Liquid (Condensation)

• What happens?
  • When a gas is cooled, its particles lose energy and move slower, allowing intermolecular forces to bring them closer together.
  • The gas then turns into a liquid.
• Example: Steam condenses into water when it touches a cold surface.

(D) Liquid to Solid (Freezing / Solidification)

• What happens?
  • When a liquid is cooled, its particles lose energy and slow down.
  • The intermolecular forces pull the particles into fixed positions, forming a solid.
• Example: Water freezes into ice at 0°C.

2. Latent Heat – Hidden Heat in State Change

Even after reaching the melting or boiling point, a substance does not change temperature immediately. Instead, the heat supplied is used to break molecular bonds instead of raising temperature. This hidden heat is called Latent Heat.

(A) Latent Heat of Fusion (Solid to Liquid)

• Definition: The amount of heat required to convert 1 kg of solid into liquid at its melting point without raising temperature.
• Why does temperature not rise?
  • The heat is used to overcome the strong intermolecular forces in solids, allowing them to break apart and become a liquid.
• Example:
  • Ice at 0°C melts into water at 0°C, even though heat is added.
  • The temperature remains constant until all ice melts.

(B) Latent Heat of Vaporization (Liquid to Gas)

• Definition: The amount of heat required to convert 1 kg of liquid into gas at its boiling point without raising temperature.
• Why does temperature not rise?
  • The heat energy is used to overcome intermolecular attraction, allowing molecules to escape as gas.
• Example:
  • Water at 100°C remains at 100°C while boiling, even though heat is continuously supplied.
  • The extra heat is used to convert water into steam.

3. Effect of Pressure on States of Matter

How Pressure Affects State Change?

• Increasing pressure brings particles closer together, strengthening intermolecular forces.
• This compresses gases into liquids or solids.

Examples of Pressure-Induced State Changes:

(A) Gas to Liquid – Liquefaction of Gases

• When high pressure is applied to a gas and temperature is lowered, it turns into a liquid.
• Examples:
  • Liquefied Petroleum Gas (LPG): Propane and butane are gases at room temperature but are compressed into a liquid inside cylinders.
  • Compressed Natural Gas (CNG): Methane gas is stored at high pressure in cylinders.

(B) Solid to Gas – Sublimation at Low Pressure

• At very low pressure, some solids directly convert into gas without passing through the liquid state.
• Example:
  • Dry ice (solid CO₂) sublimates into gas at atmospheric pressure.

Summary of Factors Affecting States of Matter