Thermodynamics Flashcards
What are the types of thermodynamic systems?
- open: transfer of E + matter possible
- closed: transfer of E possible
- isolated: no transfer possible (closed + adiabatic)
Explain the difference btw extensive and intensive variables.
Give some examples for each type.
-
extensive: depend on the size of the system,
e. g. E, m, V, Q, S -
intensive: do not depend on the size of the system
e. g. P, T, c, μ
What are the different types of transport processes by which energetic interactions (i.e. transfer of work, heat) can be effected?
- isobaric: P constant
- isochoric: V constant
- isothermal: T constant
- adiabatic: no heat transfer, ΔQ = 0
- diathermic: continuous exchange of heat
What are the reasons for internal energy U.
Give its formula.
Describe the internal energy of:
- an ideal gas w/ one atom
- an ideal gas w/ several atoms
- liquid / solid
U = Ekin + Epot (on microscopic level)
- Ekin due to translation (straight movement), vibration, rotation of atoms
- Epot due to atomic/molecular interactions
U of:
- ideal gas w/ one atom: only translational E
- ideal gas w/ several atoms: rotational, vibrational, translational E
- liquid/solid: rotational, vibrational, translational E, attractive mol. interactions
How can the internal energy U be changed?
Describe some ways.
by elementary E exchanges:
- t__hermal: change in T
- mechanical: change in P at constant V
- chemical: change in n
- surface: anisotropic behaviour on surface due to different P outside/inside → change in surface A
⇒ change of U is sum of individual elementary E exchanges
What does the 1st law of thermodynamics state?
Law of conservation of E:
E may be converted, but total E of the system remains equal
What is latent heat?
= heat of phase transition
- no change in T before state transition is completed even though heat is added
- BUT: meanwhile change in S (ΔS = heat/time)
What does the 2nd law of thermodynamics state?
entropy of an isolated system never decreases ⇒ ΔS≥0
- Smax is approached as system reaches Eq
- spontaneous proccess proceed towards most probable state (high to low)
- the only spontaneous processes that occur in an isolated system are such that equilibrate intensive variables
How can entropy S be differentiated?
Give some examples when S increases.
- thermal entropy: change in T
- conformational entropy: change of molecular order
⇒ entropy = disorder
Examples:
- increase of particle no.
- increase of T (due to increase of Ekin)
- increase of V (wider spread)
- dissociation of particles
- helix - coil transition
- melting
- mixing
NOCH AUSSTEHEND
Explain the basis of thermodynamic probability giving its formula.
What is it?
S = kB * ln W = Boltzmann constant * ln thermodynamic probability
⇒ give number of microstates for a given macrostate
- kB = universal gas constant/Avogadro’s number
What are micro- and macrostates?
Give an example.
- microstate: state of each element of the system (e.g. velocities, positions)
- macrostate: state relying on macroscopic properties (e.g. T, P, V, U, etc.)
Example:
distance btw 2 atoms (macrostate) of an enzyme remains the same altough the conformation (microstate) changes
When does the conformational enthropy increase?
when more than 1 degree of freedom
e.g. 10,000 atoms in an enzyme, each with 3 (= d.f.) possible ways of arrangement around a C-atom
S = kB * ln 10,0003
What does the 3rd law of thermodynamics state?
- S of one-component, crystallizing material at 0 K is 0
- BUT: impossible to reach T=0K in a finite no. of steps
How is the useable E at constant P called?
Give its formula.
- part of U needed to maintain isobaric situation
- enthalpy H = useable part of U
H = U + pV
ΔH = Q = heat
