States of Matter- Gases and Liquids

11th Chemistry NCERT notes

Any substance that has mass and occupies space is called Matter. The matter is composed of atoms or molecules. The force of interaction between atoms/molecules is highest in solids and least in liquids.

Interconversion of States of Matter

These states are interconvertible

  1. Melting point: This is the temperature at which a matter converts from its solid state to the liquid state. It decreases in the presence of an impurity.
  2. Boiling point: This is the temperature at which the vapour pressure of a liquid becomes equal to the atmospheric pressure. It increases in the presence of impurity and with rising in pressure. The boiling point of water is 100oC.
  3. Freezing point: At this temperature, a matter converts from its fluid state into a solid state. The freezing point of water is 0oC.

Evaporation: It is the process of conversion of a liquid into vapours at any temperature.

Interconversion of States of Matter

The temperature and pressure at which all the three states of a substance can exist together in equilibrium is called triple point, e.g., ice, liquid water and water vapours can coexist (i.e., ice ↔ water ↔vapour) at 0.0098oC and 4.58 mm.

Factors Deciding Physical State of a Substance

For the gaseous state,

The force of attraction << Thermal energy for the liquid state,

Force of attraction > Thermal energy

For solid state,

Forces of attraction >> Thermal energy


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