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Unformatted text preview: 1 CHM3400  Lecture 9 – Jan 26 3 rd Law of TD: Gibbs free energy (Chapter 4 p. 95110) • entropy as an absolute value • 3 rd Law of TD • meaning of entropy • Gibbs free energy Δ G • Dependence of Δ G on temperature and pressure • How does a refrigerator work? 2 Entropy S = k B ln(W) Entropy is an absolute value W stands for the number of microstates for a system in a given macrostate . How many microstates exist for a perfect crystal at 0 K? = → S Lim K T ∫ ∫ = = T P T P T T d C dT T C S ln 3 3 rd Law of TD “Every substance has a finite positive entropy, but at the absolute zero of temperature the entropy may become zero, and it does in the case of a pure, perfect crystalline substance.” S=0 at 0 K Phase transitions 4 Approaching zero Kelvin In reality, it is actually impossible to get down to 0 K. Current world record, see Science 301 , 2003, 1513. Because number of microstates becomes so low that cooling rate becomes very low 2500 Na atoms in a optical trap 5 Entropy change of chemical reactions aA + bB → cC + dD Hypothetical reaction: ∑ ∑ − = Δ ) tan ( ) ( ts reac S v products S v S o o o r Molar entropies at a particular temperature Stoichiometric coefficient 6 Example 4.5Example 4....
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This note was uploaded on 05/29/2011 for the course CHM 3400 taught by Professor Seabra during the Spring '08 term at University of Florida.
 Spring '08
 SEABRA
 Physical chemistry, pH

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