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Laws of Thermodynamics

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Laws of Thermodynamics for Chemical Engineers

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Laws of Thermodynamics

  1. 1. LAWS OF THERMODYNAMICS Presented by Raja Wajahat
  2. 2. • The four laws of thermodynamics define fundamental physical quantities (temperature, energy, and entropy) that characterize thermodynamic systems. • The laws describe how these quantities behave under various circumstances, and forbid certain phenomena. 2Presented by Raja Wajahat
  3. 3. ZEROTH LAW OF THERMODYNAMICS 3Presented by Raja Wajahat
  4. 4. Zeroth law of thermodynamics • If two systems are both in thermal equilibrium with a third then they are in thermal equilibrium with each other 4Presented by Raja Wajahat
  5. 5. Zeroth law of thermodynamics • The importance of the law as a foundation to the earlier laws is that it allows the definition of temperature in a non-circular way without reference to entropy, its conjugate variable. • Such a temperature definition is said to be 'empirical'. 5Presented by Raja Wajahat
  6. 6. LAW OF CONSERVATION OF ENERGY FIRST LAW OF THERMODYNAMICS 6Presented by Raja Wajahat
  7. 7. FIRST LAW OF THERMODYNAMICS • The increase in internal energy of a closed system is equal to the heat supplied to the system minus work done by it. 7Presented by Raja Wajahat
  8. 8. First Law encompasses several principles 1. The law of conservation of energy. 2. The concept of internal energy and its relationship to temperature. 3. The flow of heat is a form of energy transfer. 4. Work is a process of transferring energy to or from a system. 8Presented by Raja Wajahat
  9. 9. • Combining these principles leads to one traditional statement of the first law of thermodynamics: • it is not possible to construct a machine which will perpetually output work without an equal amount of energy input to that machine. • Or more briefly, a perpetual motion machine is impossible. 9Presented by Raja Wajahat
  10. 10. ENTROPY OF AN ISOLATED SYSTEM SECOND LAW OF THERMODYNAMICS 10Presented by Raja Wajahat
  11. 11. ENTROPY • Entropy is an extensive property. It has the dimension of energy divided by temperature, which has a unit of joules per kelvin (J K-1) in the International System of Units (or kg m2 s-2 K-1 in basic units). • But the entropy of a pure substance is usually given as an intensive property — either entropy per unit mass (SI unit: J K-1 kg-1) or entropy per unit amount of substance (SI unit: J K-1 mol-1). 11Presented by Raja Wajahat
  12. 12. SECOND LAW OF THERMODYNAMICS • The entropy of an isolated system never decreases; such a system will spontaneously evolve toward thermodynamic equilibrium, the configuration with maximum entropy. • Systems that are not isolated may decrease in entropy, provided they increase the entropy of their environment by at least that same amount. 12Presented by Raja Wajahat
  13. 13. SECOND LAW OF THERMODYNAMICS • Since entropy is a state function, the change in the entropy of a system is the same for any process that goes from a given initial state to a given final state, whether the process is reversible or irreversible. • However, irreversible processes increase the combined entropy of the system and its environment. 13Presented by Raja Wajahat
  14. 14. SECOND LAW OF THERMODYNAMICS • According to the second law of thermodynamics, in a theoretical and fictional reversible heat transfer, an element of heat transferred, δQ, is the product of the temperature (T), both of the system and of the sources or destination of the heat, with the increment (dS) of the system's conjugate variable, its entropy (S). 14Presented by Raja Wajahat
  15. 15. More on Entropy • Entropy may also be viewed as a physical measure of the lack of physical information about the microscopic details of the motion and configuration of a system, when only the macroscopic states are known. • The law asserts that for two given macroscopically specified states of a system, there is a quantity called the difference of information entropy between them. 15Presented by Raja Wajahat
  16. 16. More on Entropy • This information entropy difference defines how much additional microscopic physical information is needed to specify one of the macroscopically specified states, given the macroscopic specification of the other - often a conveniently chosen reference state which may be presupposed to exist rather than explicitly stated. • A final condition of a natural process always contains microscopically specifiable effects which are not fully and exactly predictable from the macroscopic specification of the initial condition of the process. 16Presented by Raja Wajahat
  17. 17. More on Entropy • This is why entropy increases in natural processes - the increase tells how much extra microscopic information is needed to distinguish the final macroscopically specified state from the initial macroscopically specified state. 17Presented by Raja Wajahat
  18. 18. ENTROPY AT ABSOLUTE ZERO THIRD LAW OF THERMODYNAMICS 18Presented by Raja Wajahat
  19. 19. THIRD LAW OF THERMODYNAMICS • The entropy of a perfect crystal of any pure substance approaches zero as the temperature approaches absolute zero. 19Presented by Raja Wajahat
  20. 20. THIRD LAW OF THERMODYNAMICS • At zero temperature the system must be in a state with the minimum thermal energy. This statement holds true if the perfect crystal has only one state with minimum energy. Entropy is related to the number of possible microstates according to: 20Presented by Raja Wajahat
  21. 21. THIRD LAW OF THERMODYNAMICS • Where S is the entropy of the system, kB Boltzmann's constant, and Ω the number of microstates (e.g. possible configurations of atoms). • At absolute zero there is only 1 microstate possible (Ω=1 as all the atoms are identical for a pure substance and as a result all orders are identical as there is only one combination) and ln(1) = 0. 21Presented by Raja Wajahat
  22. 22. THIRD LAW OF THERMODYNAMICS • A more general form of the third law that applies to a systems such as a glass that may have more than one minimum microscopically distinct energy state, or may have a microscopically distinct state that is "frozen in" though not a strictly minimum energy state and not strictly speaking a state of thermodynamic equilibrium, at absolute zero temperature: 22Presented by Raja Wajahat
  23. 23. THIRD LAW OF THERMODYNAMICS • The entropy of a system approaches a constant value as the temperature approaches zero. • The constant value (not necessarily zero) is called the residual entropy of the system. 23Presented by Raja Wajahat
  24. 24. Thank You! Presented by Raja Wajahat

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