MSE 3050, Thermodynamics and Kinetics of Materials, Leonid ZhigileiReview of classical thermodynamicsFundamental Laws, Properties and Processes (1)First Law - Energy BalanceThermodynamic functions of stateInternal energy, heat and workTypes of paths (isobaric, isochoric, isothermal, adiabatic, cyclic)Enthalpy, heat capacity, heat of formation, phase transformationsCalculation of enthalpy as a function of temperatureHeats of reactions and the Hess’s lawReading: Chapters 2, 6.1, 6.4 of Gaskell or the same material in any other textbook on thermodynamicsMSE 3050, Thermodynamics and Kinetics of Materials, Leonid ZhigileiThermodynamic variablesWhat are thermodynamics variables?There are two approaches to describe properties and behavior of a material: 1. Microscopic approach - to describe the material in terms of microscopic variables (positions, velocities, charges, etc. of all particles in the system). But there are too many particles (NA= 6.022×1023mol-1)and this approach in unpractical in most cases.2. Classical (continuum) thermodynamics – to describe the material in terms of average quantities, or thermodynamic variables, such as temperature, internal energy, pressure, etc.Statistical thermodynamics provides the connection between the classical thermodynamics and the behavior of the microscopic constituents of matter (atoms and molecules). Although in this course we will focus on classical thermodynamics, we will also consider a few elements of statistical thermodynamics, in particular in our discussion of heat capacity and entropy.What are state variables and functions?System at equilibrium can be described by a number of thermodynamic variables that are independent of the history of the system. Such variables are called state variables or state functions depending on the context.We can describe a system by a set of independent state variables and we can express other variables (state functions) through this set of independent variables. For example, we can describe ideal gas by P and T and use V = RT/P to define molar volume V. For different applications we can choose different sets of independent variables that are the most convenient.MSE 3050, Thermodynamics and Kinetics of Materials, Leonid ZhigileiThermodynamic variablesIntensive and extensive variablesIntensive properties – independent of the size of the system, e.g. T, P. Extensive properties – proportional to the quantity of material, e.g. V, U, C, H, S, G.Example: if V1= V2T1= T2P1= P2 then V12= V1+ V2but T12= T1= T2We can also consider “derived intensive variables,” e.g., Mass/Volume or Energy/Volume, that do not depend on the size of the system.Internal energy, heat, and work: not very rigorous definitions:It is impossible to give a rigorous definition of energy. (“...in physics today, we have no knowledge of what energy is.” - the Feynman Lectures on Physics). Thermodynamics laws do not define energy, thermodynamics is dealing with transfer of energy. In particular, the 1stlaw of thermodynamics postulates the energy conservation. In thermodynamics of materials we usually do not consider the kinetic energy of the center-of-mass motion of the system or gravitational energy (mgh), only internal energy, intrinsic to the body is considered.Internal energy U is a sum of all potential and kinetic energies in the system (not only of mechanical origin). Thermodynamics is only dealing with change of U. The absolute value of U is not defined by the laws of thermodynamics, but an arbitrary zero point is often chosen for convenience.1 2 1+2+=MSE 3050, Thermodynamics and Kinetics of Materials, Leonid ZhigileiEarly theory of heat: the caloric fluidBased on observations that heat is conserved in some cases (e.g., when mixing hot and cold water), Lavoisier proposed in 1789 that heat is transferred by weightless, conserved fluid, named caloric. French chemist Antoine-Laurent Lavoisier: “The substance of heat is a subtle fluid called caloric… the quantity of this substance is constant throughout the universe, and it flows from warmer to colder bodies.”While we know that the caloric ideas are invalid, we still say things like "heat flows“to describe the heat transferLavoisier's Table of Simple Substances (Elements) …MSE 3050, Thermodynamics and Kinetics of Materials, Leonid ZhigileiJoule's experiment: the mechanical energy can be measured simultaneously with temperature (thermal energy). Equivalence of heat and workJoule found that ¾ the loss in mechanical energy is proportional to an increase in temperature of the water and the amount of water used.¾ the constant or proportionality is 4.4 J/g ºC (modern data is 4.186 J/g ºC)Heat and work can independently produce identical changes in thesystem.T is not a good measure of heat but heat can be measured through work, and heat capacity can be determined.J. P. Joule, On the existence of an equivalent relation between heat and the ordinary forms of mechanical power, Phil. Mag. 27, 205, 1845.Heat generated from friction in cannon boring process, English physicist Benjamin Thompson: B. Thomson, Philosophical Transactions, Vol. XVIII, 286, 1798“I was struck with the very considerable degree of heat which a brass gun acquires, in a short time, in being bored; […] A thorough investigating of these phenomena seemed even to bid fair to give a farther insight into the hidden nature of heat; and to enable us to form some reasonable conjectures respecting the existence, or non-existence, of an igneous fluid: a subject on which the opinions of philosophers have, in all ages, been much divided.”MSE 3050, Thermodynamics and Kinetics of Materials, Leonid ZhigileiEnergy, heat, and work (continued)Heat is the energy being transferred to a system as a result of temperature difference (work-less transfer of internal energy).Work can be defined as the energy being transferred to a system as a result of a (generalized) force acting over a (generalized) distance.Examples of work:Mechanical work done by force F on a body moving from r1to r2along a certain trajectory or path: Work due to the volume expansion of a fluid or gas done against an external pressure P.Electric polarization work, where the generalized force is the strength of the electric field, E, and the generalized displacement is the polarization of the medium, D.Magnetic work, where the generalized force is the strength of the magnetic field, H, and the generalized displacement is the total