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Thermodynamics and Statistical Mechanics. Does the Internal Energy of a Real Gas Depend Only on Temperature?. Change of Phase. First Law is: du = đq – Pdv For a finite change at constant temperature D u = q – P D v At transition, u 2 – u 1 = l 12 – P ( v 2 – v 1 )
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Thermodynamics and Statistical Mechanics Does the Internal Energy of a Real Gas Depend Only on Temperature? Thermo & Stat Mech - Spring 2006 Class 4
Change of Phase • First Law is: du = đq – Pdv • For a finite change at constant temperature • Du = q – PDv • At transition, u2– u1 = l12– P(v2– v1) • l12 = (u2 + Pv2) – (u1 + P v1) • l12 = h2– h1 Thermo & Stat Mech - Spring 2006 Class 4
Enthalpy and Latent Heat Enthalpy is defined as: h = u + Pv Thermo & Stat Mech - Spring 2006 Class 4
Enthalpy is a State Function Thermo & Stat Mech - Spring 2006 Class 4
Does u depend on Volume? If u = u(T, v), then, Thermo & Stat Mech - Spring 2006 Class 4
From Cyclical Relation Thermo & Stat Mech - Spring 2006 Class 4
Gay-Lussac–Joule Experiment Thermo & Stat Mech - Spring 2006 Class 4
Gay-Lussac–Joule Results Thermo & Stat Mech - Spring 2006 Class 4
Joule-Thompson Throttling Process A gas passes through a constriction from a region where it is at high pressure to a region where it is at lower pressure. The gas expands, and the temperature of the gas can be lowered. This is an important tool in low temperature physics. Thermo & Stat Mech - Spring 2006 Class 4
Joule-Thompson Throttling Process Thermo & Stat Mech - Spring 2006 Class 4
Joule-Thompson Throttling Process On high pressure side: Wi = – PiVi On low pressure side: Wf = + PfVf Total work: W = PfVf – PiVi Q = 0 = DU + W 0 = Uf– Ui + PfVf – PiVi 0 = (Uf + PfVf )– (Ui + PiVi ) Thermo & Stat Mech - Spring 2006 Class 4
Enthalpy Thermo & Stat Mech - Spring 2006 Class 4
Enthalpy Thermo & Stat Mech - Spring 2006 Class 4
Enthalpy Thermo & Stat Mech - Spring 2006 Class 4
Enthalpy True for ideal gas. Thermo & Stat Mech - Spring 2006 Class 4
Ideal Gas Thermo & Stat Mech - Spring 2006 Class 4
Joule-Thompson Throttling Process Thermo & Stat Mech - Spring 2006 Class 4