Matter and its states

Matter exists in four states I.e. solid,liquid,gas and plasma. The simplest form of matter is the gaseous state and most of matter around us is in the solid state

 Propeties of gases

 Gases dont have a definite volume and occupy all the available space.
 The volume of a gas is the container. They dont have a definite shape and take the the shape of the container just like liquid.
 Due to low densities of gases , as compared to those of liquid and solids ,the gases bubble through liquids and to rise up.gases can diffuse and effuse.
This property is negligible in solid but operates in liquids as well.
 Gases can be compressed by applying a pressure because there are large empty space between their molecules.
 Gases can expand on heating or by increasing the available volume.
thomson effect 
 Liquids and solids,on the other hand,do not show an appreciable increase in volume when they are heated.when sudden expansion of gases occur cooling takes place,it is called joule thomson effect.
 Molecule of gases are in a constant state of random motion.they can exert pressure on the walls of the container and this pressure is due to the number of collisions.
 The intermolecular forces in gases are very weak.

  Properties of liquid

 Liquids dont have a definit shape but have a definit volume. Molecule of liquid are in a constant state of motion. 
The evaporation and diffusion of liquid molecule is due to this motion. 
The dendities of liquids are greater than those of gases but are close to those of solids.
 The spaces among the molecules of liquids are negligible just like solid. 
 The intermolecular attractive forces in liquids are intermediate between gases and solids. 
 Molecules of liquid possess kinetic energy due to their motion. 
 Liquids can be converted into solids on cooling I.e., by decreasing their kinetic energy.
 Molecules of liquids colled among themselves and exchange energy but those of solids can not do so. 

 Properties of solid 

 The particles present in solid substances are very close to each other and are tightly packed.
 Due to this reason solids are non compressible and they cannot diffuse into each other.
 There are strong attractive forces in solid which the oarticles toghther firmly and for this reason solid have definite shape and volume. 
 The solid particles possess only vibrational motion.

 Unit of pressure 

The pressure of air that can support 760 mm Hg coloumn at sea level is called one atmosphere. 
 It is the force exerted by 760,mm or 76 cm long column of mercury on an area of 1 cm ^2 at 0°C. The central unit of pressure is expressed in Nm^_2,  1 atm pressure I.e 760 torr is equal to 101325 Nm^_2 .