C3303 Final Flashcards
Classical thermodynamics
Relationship between mechanical and thermodynamic variables in a system
Mechanical properties
Describe composition/position (P, V)
Thermodynamic variables
Describe internal macroscopic state (U, H, A, G)
Microcanonical ensemble
System is totally isolated from surroundings; no E or matter can cross; V fixed (NVE); unrealistic
Canonical ensemble
E can transfer across boundary, but not matter; V fixed (NVT)
Isothermal-isobaric ensemble
Energy can transfer across boundary, but not matter; V can change to maintain P; (NPT)
Internal E of a system
Total E needed to create the system
Enthalpy
Total E of system and energy required to create a volume, V
Heat
Thermal E transferred from surr to sys
Work
E corresponding to expansion of system against surr
First Law of Thermo
dU=dq+dw
Entropy
change in degree of complexityE
Entropy relation
ds=dqrev/T
Hemholtz Energy
Changes in E at constant V
Gibbs Energy
Changes in E in the isothermal-isobaric ensemble at constant P
Limitations of Classical Thermo
No direct relationship between chemical structure and thermo
Ideal Gas Assumption
No intermolecular interactions
No volume
Point Masses
No potential E
Equipartition theorem
U=1/2 nDOF nRT
Degrees of Freedom (DOF)
Number of independent ways the particle can move resulting in a change to the original position
What are the 3 types of DOF?
- Translations
- Rotations
- Vibrations
Number of translations
3 (x,y,z)
Number of rotations
Linear: 2
Nonlinear: 3
Number of Vibrations
Linear: 3N-5
NonLinear: 3N-6
Why do diatomics only have 2 rot DOF?
Rotation along the bond axis does not change appearance of molecule