Topic 5B- Thermodynamics Flashcards
first law dynamics
-energy is constant
-cannot be created or destroyed
-can be converted to another or transfered from work to heat vis versa
difference between thermo and kinetics
kinetics- speed
thermo- will it take place, final, initials, spontaneous
spontaneous processes
-something that happens and we cant do anything about it eg car rusting
-spontaneous one way, but not spontaneous the other way eg egg
-temp can be spontaneous depending on different temps
Reversible vs. Irreversible
A reversible process ystem and surroundings canbe put back in their original states by exactly reversing the process- at equilibrium
Spontaneous processes are always irreversible because they naturally move toward more disorder, and reversing them requires outside energy- not equilibrium
entropy
- total microstates
-randomness and degrees of freedom
-things move from low to highm high to low requires energy
-wants to spread evenly
-state function
entropy formula
^S= S final- S initial
isothermal process
-constant temp
-heat reversed/T
-entropy increases
Second Law thermodynamics
-entropy of universe (Sys + surr) increases for spon reactions
-reversible: univ= ^Sys + ^surr= 0 (equilibrium)
-irreversible: iniv= ^Sys + ^Surr= > 0 (greater, not eq)
microstate
Temperature measures how fast molecules move (average kinetic energy).
Boltzmann imagined molecule motion like a snapshot at one moment, calling it a microstate
-amount of ways things can be places= microstate
go over molecular scale diagrams in slides
slide 19
if you had 3 atoms which had 4 J per atom and 12 12 total how many microstates would you have
-proportional (4 x 3)
-12 microstates
Molecules move in three ways:
Translational – Moving from place to place.
Vibrational – Atoms shaking within the molecule.
Rotational – Spinning around an axis or bonds
Entropy formula with microstates
w= microstates
S = k (ln W)
where k is the Boltzmann constant, 1.38 ́ 10 -23 J/K.
change in entropy:
^S = k ln W final
/W initial
entropy increase with
-number of microstates
-motion of molecules, not reversible
-when solid dissolves in solvent
-gases formed
-liquids or solutions from solids
-gas molecules increasing
-moles increasing
-molar mass
-larger more complex molecules
PHASE BEFORE MOLS G>L>S
microstates increase with
volume, temp, moving molecules
phase changes
Phase changes occur at their transition temperature are isothermal processes
-^S fus= ^H fus/ ^ Temp
-^S vap= ^H vap/ T boil
Fusion means melting
the process of a solid turning into a liquid.
-if it says liquid to solid then - fus
entropy of pure crystalline
is 0
^s ‘ formula ( from back of sheet)
=sum of prod- sum of reac
gibbs free energy
-T^Suniverse = ^H system -T^Ssystem
-T^Suniverse is defined as the
Gibbs free energy, ^G
-When ^Suniverse is positive, DG
is negative. spon in reverse
-Therefore, when ^G is
negative, a process is
spontaneous. (system)
-at 0 = equalibrium
change in gibbs (change in free energy)
-^G’= sum of reac- sum of reac
change in gibbs free energy equation when dealing with temp
^G= ^H’- T^S’
^H enthalpy term
-T^S the entropy term
change in gibbs free energy when dealing with equilibrium at standard conditions
standard conditions, 1 atm, 1 M, 25 temp
^G= ^G’ + RT Ln Q where Q=1 and Ln Q=0 so last term drops out
change in gibbs free energy when dealing with equilibrium at NON standard conditions
At equilibrium, Δ𝐺=0
therefore:
Rearranging:
ΔG ∘=−RTlnK
and
K=𝑒−Δ𝐺∘/𝑅𝑇
