Presentation of entropy


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Presentation of entropy

  1. 1. E N T R O P Y K-13ME05
  2. 2. 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 molecules.  For a given substance entropy increases as temperature is raised.
  3. 3.  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 decrease.  Total entropy of system and surrounding either remains constant or increase, (dS>0) More entropy less entropy In naturally entropy increase can’t decrease. 80’C 20’C
  4. 4. 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 decrease entropy. 0000000000000000 0000000000000000 0000000000000000 0000000000000000 00 0 0 00 0 0 00 00 00 00 0 00 00 0 00 0 00 0 00 0 0 0 00 00 00 00 00 00 00 00 0
  5. 5.  Prove entropy increase in real process:  In all natural process entropy increase so entropy cannot conserved.  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.
  6. 6.  Change in entropy .: dS=dQ/T1-dQ/T2  As, T1>T2 .: dS>0 So, in all natural process entropy tends to increase.  Unavailability:  Entropy represent the unavailability of energy, How? 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.
  7. 7. o For Carnot engine; n= (1-T2/T1)= w/Q1 Heat converted into work; W= Q1(1-T2/T1) Heat unavailable for work= Q1 .: dS=Q2/T2 Energy wasted Q2= dS.T2 If T2 is constant Energy wasted o< dS Hence amount of energy wasted is proportional to increase in entropy.