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# Entropy n process

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• 1. ENTROPY AND FOUR PROCESS
• 2. ENTROPY • • Measure of degree of Disorder or randomness in a molecular system is called ENTROPY EXAMPLES: When solid change to liquid (entropy increases). When liquid change to solid (entropy decreases). When gas change to liquid (entropy decreases).
• 3. Mathematical Expression Of Entropy Mathematical expression is Ratio of the heat change (q) to the Temperature of the reversible cyclic Process units is Cal/Deg or Jk-1 mol-1 or cal k-
• 4. Significance:  ENTROPY & UNAVAILABLE ENERGY  ENTROPY &RANDOMNESS  ENTROPY&PROBABILITY
• 5. Entropy & unavailable Energy:  When the heat is applied to system some part of system is only used to do work. It is called as available energy and remaining part of heat is unavailable energy. According to the 2nd law Entropy = Unavailable energy Temperature
• 6. Entropy & Randomness:  It is increase in entropy there is change from order state to disorder state Entropy & Probability: • A irreversible spontaneous process tends to proceed from less process to more probable state and so in spontaneous process entropy increase
• 7. Entropy changes in isothermal expansion of ideal gas According to 1st law of thermodynamic dE=q-PdV or dE=q-W (i) In reversible isothermal process change in Internal energy(dE=0) Equation (i) becomes qrev –W=0 qrev =W (ii)
• 8. The work done is expansion of moles of Gas from volume V to V at constant Temperature „T‟is W=nRT In V /V (iii) Sub(iii) in (ii) qrev=nRT In V /V We know that So, qrev = *T T =nRT In V /V = 1/T nRT In V /V 1 2 2 1 2 2 1 1 2 1
• 9. =nRTInV2/V1 =2.303nRlog V2/V1 P V =RT (or) P2V2=RT (or) 1 1 (iv) V =RT/P V2=RT/P2 1 1 =2.303nRlog P1/P2
• 10. Entropy change in reversible process (Non-spontaneous) : Consider isothermal expansion of ideal gas  If system absorbs „q‟ amount of heat from surroundings at Temperature “T” then Entropy increase of system  Entropy decrease of surrounding
• 11. Net change in entropy =q/T +(-q/T) Therefore in reversible isothermal process No change in Entropy
• 12. Entropy change in irreversible (spontaneous) Process: Consider system at higher temperature „T1‟ ,surrounding at lower temperature T2  „q‟ amount of heat passes irreversibly from system to surrounding  Decrease in entropy of system   Increase in entropy of surrounding
• 13. Net change As
• 14. Entropy change in Physical transformations : Entropy change takes place when system under goes physical transformation like vapourise fusion etc.  Let be quantity of heat absorbed in calories at constant temperature and pressure.  Entropy change  (i)
• 15. But enthalpy change (ii) L Latent heat in calories M Molecular weight in Grams T Temperature in Kelvin Sub (ii) in (i)  Latent heat of Vapourisation of H2O: 540cal /gm at 100°C Latent heat of fusion of ice: 80cal/gm at 0°C