thermochem2 Flashcards
proceeds without any outside assistance
processes that are spontaneous in one
direction are * in the
reverse direction
spontaneous process
nonspontaneous
entropy
measure of the * in a system
energy and matter tend to become more *
* function
randomness
disordered
state function
ΔS = Sfinal - Sinitial
If the change from initial to final results to an increase
in randomness:
If the change from initial to final results to a decrease
in randomness:
Sf > Si ΔS > 0 (positive)
Sf < Si ΔS < 0 (negative)
§ measures disorder
S (s) < S (l) «_space;S (g)
S (aq) usually between liq and gas
§ increases with * temperature
increasing
second law of thermodynamics:
the entropy of the universe *
in any * processes such that
increases, spontaneous
ΔSuniv > 0
a single possible arrangement of position
and kinetic energy of molecules
microstate
RELATIONSHIP BETWEEN ENTROPY AND MICROSTATES
*
S = k ln W
use statistical thermodynamics to relate bulk
properties to events on the molecular scale
à involves probabilities
à entropy increases with the number
of microstates of the system
ENTROPY ON THE MOLECULAR SCALE
* in ENTROPY • Phase change from solid to liquid. • Phase change from liquid to gas. • Phase change from solid to gas. • Solute dissolving in a solvent. • Diffusion of gases. • Increase in temperature of system.
INCREASE
When gases are involved…
Ø If a reaction produces more gas molecules than it
consumes, *
Ø If the total number of gas molecules diminishes,
*
Ø If there is no net change in the total number of
gas molecules, then ΔS0 may be positive or
negative BUT ΔS0 will be a small number.
ΔS0 > 0.
ΔS0 < 0.
the entropy of a * at absolute zero is 0
third law of thermodynamics
pure crystalline
substance
STANDARD MOLAR ENTROPY
§ reference temperature for entropy is 0 K,
so values for elements are not 0 J/mol K at 298 K
§ generally greater for * than liquids and solids
§ increases with *
§ increases with number of * in a formula
gases
molar mass
atoms
entropy changes for a reaction can be calculated in a
manner analogous to that by which DH is calculated:
where n and m are the coefficients
in the balanced chemical equation
delta S = summation (s products) - summation (s reactants)
heat that flows into or out of the system
changes the entropy of the surroundings
for an isothermal process:
delta s = q(sur)/T = -q(sys)/T
at constant pressure,
qsys is simply deltaH° for the system:
delta s = -deltaH(sys)/T
“The entropy of the universe increases in a
spontaneous process and remains unchanged in an
equilibrium process.”
Spontaneous Process: ΔSuniv =
Equilibrium Process: ΔSuniv =
Spontaneous Process: ΔSuniv = ΔSsys + ΔSsurr > 0
Equilibrium Process: ΔSuniv = ΔSsys + ΔSsurr = 0
the maximum amount of useful work which
can be extracted from a closed system
formula
gibbs free energy
G = H – TS
ΔGº = ΔHº - TΔSº
mem
is the process spontaneous? ΔGº forward reaction is spontaneous ΔGº the system is at equilibrium ΔGº forward reaction is nonspontaneous (but spontaneous in the reverse direction)
is the process spontaneous? ΔGº < 0 forward reaction is spontaneous ΔGº = 0 the system is at equilibrium ΔGº > 0 forward reaction is nonspontaneous (but spontaneous in the reverse direction)
analogous to standard enthalpies of formation
are standard free energies of formation, ΔGºf:
formula
copy
ΔfGº for an element is *!
zero
free energy function is also dependent on *
in certain instances, reactions can be
product−favored at equilibrium at one temperature
and reactant−favored at another
temperature
spontaneity of a process can be predicted
from the signs of DH and DS
table
