Class IX, CHEMISTRY, "States of Matter"

States of Matter

Matter has three states:
1. Gas
2. Liquid
3. solid
These are physical states of matter. The three states of one matter may have different physical properties while their chemical properties are same. Water exists in three physical states solid (ice), liquid and gas(steam) has same chemical properties.

Kinetic Theory of Matter

The Kinetic theory was presented to explain the properties of gases and is called kinetic theory of gases. But this theory was also able to explain the composition of liquid and solid state of matter. So its is called Kinetic Theory of Matter.
According to Kinetic Theory of matter:
1. All matter is composed of atoms, molecules or ions.
2. These particles have kinetic energy due to which they are in the state of motion.
3. In gaseous state, these particles move in a straight line. They collide with one another and with the walls of container. In liquids the rate of their movement is very small but in solids, there is to and fro motion only.
4. Generally material particles can have three types of movements, i.e. translational, rotational and vibrational.

Solids

The state of matter which has definite shape and volume is called solid.

Properties of Solids

1. Definite Volume and Shape
The cohesive forces in solid substances are so strong that they keep their particles arranged in fixed positions. So due to restrict movements of particles, the solids have definite volume and shape.

2.Motion of Particles
The solid particles have vibrational motion only because these particles are held in fixed position by strong cohesive forces.

3. Effect of Heat
The physical state of solid substance can be changed by heating. On heating solid is converted to liquid and gaseous state. Heat increases the kinetic energy of the particles and they start vibrating at higher frequency. At a particular temperature the vibrational motions become fast that they overcome the cohesive forces and solid melts to liquid.

4. Melting Point
The temperature at which the solid is converted to liquid on heating is called melting point. At melting point, the particles of solid loose their means position and their arrangement. The solid collapses and turns to liquid.

5. Sublimation
The conversion of some solids directly into gaseous state on heating is called sublimation. Iodine, ammonium chloride and naphthalene change directly into vapour state upon heating.

Liquid

The state of matter having definite volume but indefinite shape is called liquid.

Properties of Liquid

1. Volume
Liquids have definite volume. In liquid particles are very close to one another and have cohesive forces among the particles. Due to the presence of cohesive forces, liquids have definite volume and keep their level as well.

2. Shape
Liquids do not have any specific shape. They adopt the shape of the container. The molecules of liquid are able to move. Due to this random motion the molecules of liquid do not have fixed position and as a result, a liquid does not have any specific shape.

3. Evaporation
Conversion of liquid into its vapours at any temperature is called evaporation. The molecules of liquid come to the surface of liquid and escape by overcoming cohesive forces. So liquid is converted to vapours at all temperature.

4. Boiling Point
The temperature of a liquid at which its vapour pressure becomes equal to the atmospheric pressure is called boiling point.

Gas

The state of matter which does not have definite shape and volume is called gaseous state.

Properties of Gaseous State

1. Indefinite Volume and Shape
In gaseous state, the molecules have insignificant cohesive forces among themselves. They move very fast in all possible directions. As a result, a gas neither has fixed shape nor a fixed volume.

2. Kinetic Energy of the Particle of a Gas
Gas particles have very high kinetic energy as compared to liquid and solid state.

3. Pressure
The molecules of a gas are in the state of random motion. The molecules of gas not only collide with one another but also with the walls of the container in which they are enclosed. Due to their collision, the velocity of the molecules changes every moment. The pressure exerted by gas is also due to the collision of its molecules with the walls of the container.

4. Elastic Collision
The collision of gas molecules is elastic in nature which means that the total energy of the colliding molecules remains the same before and after the collision.

5. Kinetic Energy
The kinetic energy of molecules of gas is very high as compared with solid and liquid.

Diffusion

The movement of molecules from a higher concentration to a lower concentration is known as Diffusion.
If the concentration of molecules at a particular place is higher, they start moving towards a place where their concentration is lower. When the concentration of molecules at both the places becomes equal the process of diffusion stops.

Diffusion in Gases

The molecules of one gas can diffuse easily into the molecules of other gas. For example if an open bottle of a perfume is kept in a room, its smell will spread uniformly throughout the room. The liquid perfume present in the bottle volatilized slowly and its vapours diffuse through out the room.

Graham’s Law of Diffusion

Scottish Chemist, Thomas Graham (1833) discovered that lighter gs can diffuse through porous pot faster than the heavier one. This is called Graham’s

Law of Diffusion.
Hydrogen being lighter gas will diffuse faster than oxygen or carbon dioxide.

Diffusion in Liquids

Liquid molecules can also diffuse because they have free movement. Since the molecules of liquid move comparatively slowly than gas molecule, their rate of diffusion are also lesser than gases.

Brownian Movement

Robert Brown (1927) discovered this phenomenon:
The free movement of the molecules of gases and liquid is called Brownian Movement.”

When a pollen grain is put in water. The movement of pollen grain in water is observed by microscope. It is observed that pollen grain is continuously moving in all directions. This free movement of pollen grain was due to the free movement of water molecules. The colliding water molecules will also force pollen grain to move as well. The students can observe Brownian movement with the help of simple experiment.

Experiment

Put a drop of milk on a microscope slide and cover it with cover slip. Put it under microscope and observe it. You will see small particle of fat moving randomly in milk. The movement of fat particles is actually due to the movement of water molecules in milk.