8 second law of thermodynamics : states spontaneous process is always accompanied by an
increase in the total entropy of the systems and its surroundings .
To take another example of disordering , the melting and boiling of zinc , at its melting
temperature the closed backed hexagonal crystal structure of zinc becomes slightly broken
up to produce a liquid with an entropy increased of 10.5J .At its boiling point the liquid
structure is completely destroyed to form the completely random gaseous phase and the
entropy increase by 96j/k. we know that the change in the state of ordere of the system at
the boiling point is much greater than at the melting point and this is reflected in the very
much larger entropy change on boiling.
S.Carnot proposed a theorem which stated that all machines working thermodynamically
reversibly in cycles between the same temperatures of source and sink have the same
efficiency . by thermodynamically reversible working. The temperature of source and sink
refer in the case of a steam engine to the temperature of the system supplied to the engine
and the temperature of the steam when the engine has completed its work nrespectively.
Efficiency of the heat engine =(T1-T2)/T1
The ratio of the heat absorbed by a system to the temperature at which it is absorbed
entropy change.it is an extensive property of the system as it depends on the mass of the
system and is a thermodynamic variable depending on the state of the system not on the
history .