DEVIATION FROM IDEAL BEHAVIOUR IN TERMS OF INTERMOLECULAR FORCES AND MOLECULAR SIEE, DEVIATION AT HIGH PRESSURE,

 DEVIATION FROM IDEAL BEHAVIOUR IN TERMS OF INTERMOLECULAR FORCES AND MOLECULAR SIEE:

             As a general gas equation is used to check the non-ideal behavior of gases. The general gas equation is based upon the kinetic theory of gases. Two postulates of kinetic theory of gases are wrong. Two postulates which explain this non-ideal behavior of real gases are given below. The two wrong assumptions are;

 (a)       There are no forces of attraction or repulsion among the gas molecules.

(b)       The actual volume of gas molecules is negligible as compared to the volume size non polar molecules. Among He, H₂, NH₃, CO₂ and N₂ gases. Ammonia, NH3 is a polar molecules which shows highest degree of deviation similar other gases show deviation according to their molecular size i-e; large size molecules show more deviation than small size molecules.  The order of deviation at high pressure or at low temperature is given below;

             NH₃ > CO₂ > N₂ > H₂ > He

 CONDITIONS NECESSARY FOR A REAL GAS TO APPROACH IDEAL BEHAVIOUR:

             For a real gas to behave like ideal gas two conditions are necessary.

 1^st Condition:

            There should be no attractive or rupsive forces among gas molecules.

 2^nd Condition:

            The volume occupies should be large enough so that actual volume  could be neglected as compared to volume occupied by the gas molecules. Both condition could be achieved by using very Low pressure or  at very High pressure. Under such conditions the real gas molecules get maximum separated from each other. As a result the intermolecular occupied by the gas molecules.

 DEVIATION AT HIGH PRESSURE:

             At high pressure the gas molecules come closer to each other and will occupy smaller volume. Under such conditions Van der waals, forces of attraction become dominant. Similarly due to close packing the collision become more frequent hence actual volume become significant which could not be ignored.

 DEVIATION AT LOW TEMPERATURE:

             At low temperature attractive forces between the gas molecules cannot be ignored because at low temperature molecules lose their kinetic energy come  closer to each other and van der waals, forces of attraction become dominant. Moreover less volume is occupied by the gas, hence actual volume does not remain negligible as compared to the volume occupied by the gas molecules.

 DEVIATION OF POLAR MOLECULES:

             Polar molecules show more deviation from ideal behavior as compared to non-polar molecules because polar molecules have dipole – dipole intermolecular forces among them. Among non-polar molecules, large size molecules show more deviation than small size non-polar molecules because large size non polar molecules have more dominant temporary dipole – induced dipole attractions as compared to small forces not having a chance to work effective. Similarly due to large spacing in the given volume number of molecules are in very small proportion. Hence, actual volume could be ignored as compared to volume occupied by the real gas molecules at very low pressure or at very high temperature. Experimentally it is observed that hydrogen gas, H₂ and helium gas. He behave as ideal gas at very low pressure and at very high temperature.

 LIQUID STATE:

             The state of matter which have definite volume but indefinite shape is called liquid state. On the basis of kinetic molecular model the liquid state have the following general properties.

 (1)              Intermolecular forces of liquids are greater than those of gases.

(2)              Liquid molecules move randomly in a zig – zag manner which is known as Brownian motion.

(3)              Molecules of liquid arrange themselves in order but there is short – rang order and long range disorder i-e; no fixed arrangement of molecules.

(4)              The molecules of liquid evaporate from the surface of the liquid at all temperatures.

(5)              The liquids are intermediate in character between solids and gases.

 TYPICAL PROPERTIES OF LIQUIDS:

             On the basis of kinetic molecular model of liquids the following typical process could be explained i.e; melting vaporization and vapour pressure.

 MELTING:

             In solids the kinetic energy of the particles is not enough to overcome the intermolecular forces completely. As a result the particles are held in a fixed pattern. When solid is heated the particles gain more kinetic energy until the kinetic energy is sufficiently high to overcome the attractive forces in a crystal lattice hence, the solid melts into liquid state.

VAPORIZATION:

             As particles of liquid are constantly moving and colliding hence, there is a continuous interchange of energy among the particles. As a result some of the molecules get more kinetic ebergy than the others. The molecules with sufficiently higher kinetic energy overcome the attractiveforces of liquid and escape as vapour thus the process of conversion of liquid molecules into vapours is called vaporization and it takes place at all temperatures but vaporization takes place at faster rate at higher temperatures.