MS811Material Thermodynamics (3 Credit Hours Course) Prof. Nasir Ahmad Lecture 6-Mostly Revision for Exam: Wednesday, 25 November 2009 Lecture 7-Carnot Cycle: Wednesday, 2 nd December 2009 Contact: Office Phone: ME –Material Thermodynamics-811-Lecture Notes-FALL2009- (Dr. Nasir Ahmad)

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MS 811 (3 CH) Material Thermodynamics  Course Contents: Concepts of Helmholtz Free Energy and Gibbs Free Energy, Energy-Property relationships, Thermal Equilibria, Chemical Equilibria, Ellingham Diagrams, 1 st order and 2 nd order Transformations, Gibbs Helmholtz Relationships, Fugacity and Chemical activity, Equilibrium constant and its variation with temperature, Vant Hoff’s equation, Effect of temperature and pressure on phase transformations, Clapeyron equation, Thermodynamics of solutions, Gibbs- Duhem relationship, Thermodynamic properties and equilibrium phase diagrams, Mixing functions, Excess functions, Phase Rule, Gibbs free Energy and Entropy Calculations of Phase transformation, Typical Equilibrium Phase Diagrams, Statistical Methods in thermodynamics.  Reading:  Thermodynamics of Materials (David V. Ragone)  Introduction to Thermodynamics of Materials (D. R. Gaskell)  Thermodynamics, an Advanced Text for Material Scientists (J. Hudson) 3

Equation of State  From First Law  We also know, 4

 Useful Approximation of of heat capcities of elemental gases at low pressure.  For a monoatmic ideal gas, such as Helium  R is a constant, equal to joules per Kelvin or calories per degree Celsius, that is the constant of proportionality (R) in the equation Pressure × Volume = n (number of moles) × (R) × Temperature, relating the pressure and volume of a quantity of gas to the absolute temperature. 5

First Law of Thermodynamics  Conservation of Energy  Says Nothing About Direction of Energy Transfer

Second Law of Thermodynamics  Preferred (or Natural) Direction of Energy Transfer  Determines Whether a Process Can Occur

Second Law of Thermodynamics  Three Types of Thermodynamic Processes  Natural (or Irreversible)  Impossible  Reversible

Natural (or Irreversible) Process  Physical Processes That Proceed in One Direction But Not The Other  Tends Towards Equilibrium  Equilibrium Only At End of Process

Natural (or Irreversible) Process  Examples  Free Expansion of Gas Valve Closed Vacuum Gas

Natural (or Irreversible) Process  Examples  Free Expansion of Gas Valve Open Gas Increase in Entropy Equilibrium Gas

Natural (or Irreversible) Process  Examples  Thermal Conduction HotCold dQ

Natural (or Irreversible) Process  Examples  Thermal Conduction Warm Increase in Entropy Equilibrium

Natural (or Irreversible) Process  Examples  Conversion of Potential & Kinetic into Internal Energy Steel Ball

Natural (or Irreversible) Process  Examples  Conversion of Potential & Kinetic into Internal Energy Inelastic Collision Warmer

Natural (or Irreversible) Process  Examples  Conversion of Potential & Kinetic into Internal Energy Inelastic Collision Tends Towards Equilibrium Increase in Entropy Warmer

Natural (or Irreversible) Process  Equilibrium  Time independent  Properties do not change with time Valve Open Gas Gas Warm Warmer

Impossible Process  Physical processes that do not occur naturally  Process that takes system from equilibrium

Impossible Process  Examples  Free Compression of Gas Valve Open Gas Gas

Impossible Process  Examples  Free Compression of Gas Valve Open Vacuum Gas Decrease in Entropy

Impossible Process  Examples  Thermal Conduction Warm

Impossible Process  Examples  Thermal Conduction HotCold Decrease in Entropy

Impossible Process  Examples  Conversion of Potential, Kinetic and Internal Energy Warmer

Impossible Process  Examples  Conversion of Potential, Kinetic and Internal Energy Decrease in Entropy Warmer

Impossible Process  Cannot Occur without Input of Work dW

Impossible Process  System’s Entropy Decreases  Total Entropy Increases dW Decrease in Entropy Increase in Entropy Environment

Reversible Process  Reversal in direction returns substance & environment to original states

Reversible Process  A conceptual process  Idealized version of how things should be  No processes are truly reversible

Reversible Process  Useful concept  Helps investigate Second Law and Entropy

Reversible Process  Conditions that aid a reversible process  Process occurs slow enough  Each state of the system is in an equilibrium  State variables reach equilibrium

The Second Law of Thermodynamics and Entropy  Distinction between a reversible and an irreversible process:  reversible – one can reverse the process and cause the system and the environment both to return to their original condition  irreversible – one can reverse the process and cause the system to return to its original condition, but the environment will have suffered a change from the original condition