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Entropy

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Entropy

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Entropy

  1. 1. SEMINAR ON ENTROPY
  2. 2. CONTENTS • INTRODUCTION • VARIOUS TYPE OF DISORDER • EXAMPLES OF DISORDER • DEFINITION AND EXPRESSION OF ENTROPY • IMPORTANCE OF ENTROPY IN GEOCHEMICAL THERMODYNAMICS • APPLICATION OF ENTROPY • CONCUSION • REFERENCE
  3. 3. INTRODUCTION What is entropy?  The word entropy is sometimes confused with energy. Although they are related quantities, they are distinct.  or energy measures the capability of an object or system to do work.  on the other hand, is a measure of the "disorder" of a system. What "disorder refers to is really the number of different microscopic states a system can be in, given that the system has a particular fixed composition, volume, energy, pressure, and temperature. By "microscopic states", we mean the exact states of all the molecules making up the system. Entropy = (Boltzmann's constant k) x logarithm of number of possible states = k log(N).
  4. 4. Entropy - thermodynamic property-- a quantitative measure of disorder Entropy traces out its origin –molecular movement interpretation-Rudolf Clausias in 1850 The concept of entropy -thermodynamic laws(i.e. the 2nd law of thermodynamics) It can be visualised due to the process of expansion, heating, mixing and reaction. Entropy is associated with heat and temperature.
  5. 5. Entropy-reflects the degree of disorderness. Diorderness can be pointed out in three different types. They are: Positional disorder whether the atoms are free to move or not Vibrational disorder(thermal disorder) whether the atoms vibrate about an average position Configurational disorder this refers to the distribution of different atoms or sites in lattice. Various types of disorder
  6. 6. EXAMPLES OF DISORDER
  7. 7.  This is one example of entropy  Box 1-less entropy  Box 2-more entropy Box-1 Box-2
  8. 8. Definition and expression of entropy Entropy may be defined as the property of a system which measure the degree of disorder or randomness in the system  It is a Greek word which means transformation  It is denoted by the symbol ‘S’ Clausius was convinced of the significance of the ratio of heat delivered and the temperature at which it is delivered,
  9. 9. Entropy is the sum total of entropy due to positional disorder, vibrational disorder and configurational disorder. i.e randomness due to change of state S=sp+st+sc
  10. 10. When a system is undergoing change then the entropy change is equal to the heat absorbed by the system divided by the temperature at which change taken place. ΔS = S2 –S1 = ∫ dq / T T ΔS = dq or TdS = dq this is the II law expression. Suppose the process is undergoing change at constant temperature:
  11. 11. From I Law we know that ΔE = q – w or dE = dq – dw or dE = dq – PdV At constant temperature ΔE = 0, therefore dq = PdV. From II law we know that dq = TdS , Substituting this in the above we get, Tds = Pdv ΔS = PdV / T,
  12. 12. Suppose the process is undergoing change at constant pressure condition then: T ΔS = (q)p - but we know that (q)p = CpdT T ΔS = Cp dT, Or TdS = Cp dT By integration, 1∫2dS = 1∫2 Cp dT /T S2 – S1 = Δ Cp ln (T2 / T1) This is the entropy change of the system at constant pressure condition from room temperature to the reaction temperature.
  13. 13. Importance of entropy in geochemical thermodynamics The aim of the thermodynamics in geochemical term is to generate a set of properties, which helps us to predict the direction of chemical processes. The 2nd law starts with simplest term is that there is an increase in entropy in every natural processes. The degree of order or disorder in a system may be described in terms of the probability or improbability of the observed state,
  14. 14.  With the statistical conception of entropy, the possible application to geochemical systems become recognisable,  For e.g.- the distribution of energy in geomorphic system is one way of expressing the relative elevation of particle of water and sediments etc. in the evolution of landscape.  It is noted that all natural processes are spontaneous, unidirectional –where there is increase in randomness.  Thus this disorderness in the geochemical processes can be determined by the concept of entropy
  15. 15. Applications of entropy Thermobarometric models Experimental work in the mineralogy, petrology etc. Thermobarometric models are various thermodynamic formulas or equation by which pressure temperature are determined, The model is calibrated through experimental techniques
  16. 16. Thus entropy is applied in the model to measure the disorderness of the system through temperature , pressure of the rock. Thermobarometry is thus an excellent case study when the application of the thermodynamic parameters are involved
  17. 17. Conclusion Entropy is the thermodynamic property which is the measure of disorder in a system. It can be expresses by ‘S’=q/t The term is coined by Rudolf Clausius. Entropy is mainly associated with heat and temperature. Disorder can be of 3 types- Positional, Vibrational and Configurational Thermobarometric models is an excellent case study when the application of thermodynamic parameters are involved.
  18. 18. It can also be concluded that- (a) when heat is transferred at a high temperature, entropy change is small whereas when heat is transferred at low temperature, entropy change is greater. (b) When heat is supplied-entropy increases and when heat is removed- entropy decreases Entropy is not perceptible to our sense and there is no such instrument to measure its effect. Only changes in entropy can be determined by computations. It is usually determined from some specified arbitrary datum of temperature only.
  19. 19. References  Alok K.Gupta and Sisir K. Sen, a short course on elementary thermodynamics for earth scientist,96  Guirlo Ottonello, principles of geochemistry, Columbia University press, New York, 1893, 151  Roger Powell, equilibrium thermodynamics in petrology,Hasper and row publishers, pp 231-232  W.M White, geochemistry, 2007, pp 44-54  www.google.com  www.wikepedia.org

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