CHEM 1B Lecture 9: Lecture 9 Thermodynamics
Document Summary
Higher external pressure = more work needs to be done. External pressure can"t be bigger than internal pressure for system to do work. Pex = pin = p (same intial and final states as free expansion. Wrev = -nrt ln (vf/vi) = -qrev ( reversible, isothermal expansion does maximum work ) = -2. 0 mol x 8. 314 j k-1 mol x 298 k x ln (1. 4 l/0. 5l) =-12. 0 atm x 0. 9 l = -10. 8 latm = -1090 j. S has units of j k-1 : dispersal of energy per unit temperature. Constant t: s is related to energy transferred reversibly as heat. S = qrev/t for a given qrev, s is larger at lower t. Changes in t leads to a change in entropy. Change in v leads to a change in entropy e. g. isothermal expansion of ideal gas. Example: entropy change due to a change in volume. S is measure of energy dispersal/disorder in the system.
