Gases are the substance in which the particles are very loosely packed and can compressed. Gases like LPG and CNG are compressed in cylinders and are used as fuels.
- Any substance that has weight and occupies space is called matter. Matter exists in three states: solids, liquid and gases.
- The molecules of solids are very closely packed with strong forces of attraction between them. They cannot move about freely.
Solids have fixed shapes and volumes.
- The molecules in the liquid are loosely packed with weak forces of attraction. They move about more freely than in solids. Liquids have fixed volume but no fixed shape. They take up the shape of the container in which they are poured.
- In gases the molecules are very loosely packed. They have very weak forces of attraction between them. Gases do not have fixed shape or volume. They occupy all the available space.
- The different states of matter are interchangeable. When solids are heated they become liquids. When liquids are heated they become gases. When gases are cooled they become liquids, which upon further cooling become solids.
- Solids dissolve in liquids. The substances which dissolve in a liquid are called soluble and those which do not, are called insoluble.
- The substance which dissolves is called a solute. The substance in which the solute dissolves is called solvent. The combination of solute and solvent is called solution.
For example, when sugar dissolves in water it forms sugar solution. The solute is sugar and the solvent is water and the solution is sugar solution.
- When things dissolve, the solute particles occupy the small spaces present between the molecules of the solvent. Even some gases like oxygen and carbon dioxide dissolve in water.
- Undissolved substances can be separated from the solvent through filtration.
- Dissolved substances can be separated by evaporation. When a solution is heated, the solvent evaporates and the solute is left behind. Common salt is obtained by the evaporation of sea water.