Lecture 5

Readings

http://umdberg.pbworks.com/w/page/104869513/Example%3A%20Arranging%20energy%20and%20entropy

http://umdberg.pbworks.com/w/page/104797843/Biological%20Consequences%20of%20the%20Second%20Law%20of%20Thermodynamics

Arranging Energy and Entropy

• The 2nd law says the system will move toward the macrostate with the greatest number of microstates

  

• So the system will move toward the situation ( the macrostate on the right )

• Rule: Microstates multiply

• Rule: Entropy adds

• $S=k_B\ast ln(W)$$S = k_B * ln(W)$

• How many microstate for:

• For top material: 4 ways to arrange 3 energy into 4 degrees of freedom
• For bottom material, 4 ways to arrange 1 energy into 4 degrees of freedom
• So total number of microstates = $4\ast 4=16$$4 * 4 = 16$

Entropy and Biology

• Thermal equilibrium = death

• Maintaining differences - temperature, pH , concentrations - is usually a matter of maintaining a lower entropy, a disequilibrium

  • I say usually because sometimes, apparent order is favored by the 2nd law, such as when oil and water separate

• Local entropy can decrease ( for example for an organism ), but only if the entropy of the universe as a whole increases

• I like the though of life existing because we dip into the flow of energy from the sun, using that energy to maintain our lower entropy