Thermodynamics and Statistical Mechanics The Third Law of

Thermodynamics and Statistical Mechanics The Third Law of Thermodynamics Thermo & Stat Mech Spring 2006 Class 10 1

Statements of Third Law All reactions in a liquid or solid in thermal equilibrium take place with no change of entropy in the neighborhood of absolute zero. (Nernst) The entropy of a true equilibrium state of a system at absolute zero is zero. (Planck) Thermo & Stat Mech - Spring 2006 Class 10 2

Statements of Third Law It is impossible to reduce the temperature of a system to absolute zero using a finite number of processes. (Unattainability statement) Thermo & Stat Mech - Spring 2006 Class 10 3

Entropy Thermo & Stat Mech - Spring 2006 Class 10 4

Nernst Postulate Thermo & Stat Mech - Spring 2006 Class 10 5

Planck Thermo & Stat Mech - Spring 2006 Class 10 6

Equivalence of Statements Assume that the unattainability statement of the third law is valid, and show that it leads to the Nernst statement. DS 0 = S 01 – S 02 = 0 Thermo & Stat Mech - Spring 2006 Class 10 7

Equivalence of Statements Consider adiabatic cooling Thermo & Stat Mech - Spring 2006 Class 10 8

Adiabatic Cooling Plot Thermo & Stat Mech - Spring 2006 Class 10 9

Can Achieve T = 0 Thermo & Stat Mech - Spring 2006 Class 10 10

Real Cooling Thermo & Stat Mech - Spring 2006 Class 10 11

Consequences of Third Law Thermo & Stat Mech - Spring 2006 Class 10 12

Consequences of Third Law Clausius-Clapeyron equation Thermo & Stat Mech - Spring 2006 Class 10 13

Consequences of Third Law Thermo & Stat Mech - Spring 2006 Class 10 14