Entropy or Change of System:
Amount of heat (Q) added to or removed from a
system divided by temperature (T).
It is measure of disorderness of system.
It is denoted as dS and dS=dQ/T (unit J/K).
Unavailability of useful energy is called Entropy.
Entropy of gas and liquid is greater than solids.
Larger molecules have larger entropy than smaller
For a given substance
entropy increases as
temperature is raised.
Entropy is directly proportional to ratio of
heat and temperature, either dQ or T
increases entropy will definitely increase.
Entropy of isolated system may increase but can never
Total entropy of system and surrounding either
remains constant or increase, (dS>0)
More entropy less entropy
In naturally entropy increase can’t
Blue ball Black ball
In order (Less entropy ) Disorderness (More entropy)
Due to increase in disorderness entropy increase.
It is impossible to regain the original position of ball to
00 0 0 00 0 0 00 00
00 00 0 00 00 0 00 0
00 0 00 0 0 0 00 00
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Prove entropy increase in real
In all natural process entropy increase so entropy
Let suppose a body at temperature T1 radiate always a
small heat dQ.
A cold body B at temperature T2 receive that heat.
If dQ be so small that T1 and T2 are not altered then,
Entropy A decrease by –dQ/T1.
Entropy of B increased by dQ/T2.
Change in entropy
As, T1>T2 .: dS>0
So, in all natural process entropy tends to increase.
Entropy represent the unavailability of energy,
Entropy is measure of capacity to do work or a system at
a higher temperature will tend to do work or transfer
of heat to its lower temperature, surrounding In the
process entropy increases,
Greater the entropy, the less available is the entropy.
o For Carnot engine;
n= (1-T2/T1)= w/Q1
Heat converted into work;
Heat unavailable for work= Q1
If T2 is constant
Energy wasted o< dS
Hence amount of energy wasted is proportional to
increase in entropy.