University:
The Pennsylvania State University
Course:
CHEM 450 | Thermodynamics
Academic year:

2024
Views:

166

Pages:

2
Author:

Alexis H.

Entropy Spontaneous process - direction of change that does not require work, W, to bring it about Example: drop a hot piece of iron into a lake (infinite heat bath); the iron will spontaneously cool to the temp of the lake (heat dispersion) Example: drop a rubber ball onto a table (heat dispersion) Non-spontaneous processes require input of work to occur Kelvin statement - no process is possible that solely converts heat to work 2nd law - things tend toward disorder Statistical view of entropy — flip a coin 4 times I I 6 HHHH TTTT HHHT HHTH HTHH THHH HTTT THTT TTHT TTTH HHTT. HTHT. THHT. TTHH THTH HTTH 5 t.mka.ba 4 3 2 1 4:0 3:1 2:2 1:3 0:4 Molecules are even less likely to differ from most probable state S = kB ln ! Statistical definition S - entropy function k(B) - Boltzmann's constant W- number of possible arrangements For a spontaneous change: ¢Stotal > 0 Stot = Ssys + Ssurr Note: irreversible processes are spontaneous and Free expansion (no work done) Disorderly vs. Orderly transfer of energy ¢Stotal > 0 Work - orderly transfer of energy and the entropy does not increase Heat - disorderly transfer of energy and entropy does increase Thermodynamic definition of entropy dqrev T dS = ¢S = Z f i dqrev T Difference in entropy between two states is calculated along the reversible pathway Isothermal expansion - need to calculate change in entropy along reversible pathway (Pin = Pout at every step) Note: adding heat at low temperature causes a greater increase in entropy than doing the same at high temp Systems at lower temp occupy few states, so adding energy makes more difference Units of entropy: J/K Same as heat capacity