Van der waal force include all intermolecular forces that
act between electrically neutral molecules. it is the negligible force that hold molecules of gas at same place
before any amount of energy ( increase in individual kinetic energy of
molecules) disperse them. in liquid for example , it is the force that hold water
molecules together before being dispersed into steam at boiling point.
Certain assumption
are made in the derivation of the ideal gas equation, PV=nRT, below are some of
the assumption made and cannot be valid are according to van der waal
·
the volume of the gas cannot be negligible in
respect to the volume of the containing vessel.
·
the force of attraction between the gaseous
molecules cannot be negligible as postulated in the kinetic theory.
with real gases, the relation PV=nRT, fails at high pressure
and low temperature, to account for the above observations , some correction
are made to the ideal gas relations, PV=nRT as follows.
the correction for
the volume of the gas molecules is taken into account by changing the volume
V →v-b, where b is
the volume of the gas molecules.
the correction for the attractive force is accounted for by
adding a/v2 to the pressure , where a is a constant, therefore the
van der waal equation for real gases
becomes
( p + a/v2 )(v-b)=RT
( p + a/v2 )(v-b)=nRT for n moles of gases
No comments:
Post a Comment