Thermodynamics Flashcards
What is a spontaneous change?
A change that happens on its own, without the need of energy from outside the system. (theres an exception)
Whats the exception to the “concept” of energy free spontaneous change?
sometimes activation energy is required to initiate a spontaneous change
If a change is ——- in one direction, it will be ———– in the reverse direction
spontaneous
non-spontaneous
non-spontaneous reactions and processes may be ______ with……..
driven
continual input of energy
Many exothermic processes are……
spontaneous
are instant ice pack reactions exo or endo? are they spontaneous?
It is exo as heat is being released into the surrounding
yes it is spontaneous, the chemical reaction doesn’t need energy to happen.
Is ice melting exo or endo? is it spontaneous?
it is endo as heat is being absorbed into the ice cube.
yes it is spontaneous
Dissolution and ice melting is usually what type of transformation
endothermic
what does an increase in freedom of motion of particles in a system indicate
more space to move so favoring spontaneity
The measure of energy dispersal and freedom of motion in a system is called
entropy
unit denoted for entropy
S
Positive ΔS indicates
increased dispersal (of energy)
Negative ΔS indicates
decreased dispersal (of energy)
whats a life hack way to think about entropy
more entropy = MORE RANDOMNESS
ΔS formula
Sfinal - S inital
ΔS unit
J/K
S° (standard molar entropy)
entropy of 1 mole of the pure substance in its standard state
Entropy is correlation with bond ______ in STATES
tightness
solid STATE has ______ bond so entropy is ______
tighter
less
but don’t confuse tighter bonds as more molecules.
More molecules means
more entropy
“more energy disperse = more entropy” is waht
when more molecules have higher entropy than less molecules
More flexible and complex chemicals means
more entropy
what is the dominating effect of molecular complexity
the physical state
When does the complexity and flexibility of chemicals hold true (only 1 scenario)
WHEN SUBSTANCES ARE IN THE SAME STATE
s < l < g which way does entropy arrow point
right
As temperature increases, entropy will also
increase
are jumps for states due to temperature on a graph continuous
no they are discontinous
the cyclic forms of molecules are closed off and rigid, so they are…… (2 diff sayings)
conformationally restricted
entropically disfavored
Does salt gain or lose entropy when dispersed
gain
Does water gain or lose entropy when dissolving something, why?
loses entropy as its ordered around the ions
Net entropy change depends on what
relative magnitudes of entropy changes in both solute and solvent entropy
Why does increased entropy favour spontaneous change
High entropy configurations can be achieved in more ways than low entropy configurations so its more likely to occur
Absolute entropies can be calculated from # of ________
microstates
Spontaneity seems to be promoted by an ________ in __________
increase
entropy
Does the sign of ΔS for a system’s transformation predict the direction of a spontaneous reaction
NO
example of why spontaneity can not be predicted by the sign alone
Ice melts SPONTANEOUSLY at high temps
water freezes SPONTANEOUSLY at low temps
FIRST law of thermodynamics
the energy in the universe remains constant
SECOND law of thermodynamics
Spontaneous reactions proceed in the direction that INCREASES the entropy of the universe
ΔS univ = ΔS sys + Δsurr > 0
this is what
second law of thermodynamics formula
any decrease in the entropy of the system must be OFFSET by what so that the process remains spontaenous
larger increase in entropy of surroundings for that process to remain spontaneous
2nd law’s implications (2)
isolated systems always evolve toward higher-entropy states
the energy of the universe is always increasing
What concepts does the 2nd law link together
heat flow and temperature
how is temperature and heat flow linked (something to do with the AMOUNT of change in entropy)
if T is very low –> change in entropy can be HUGE (way more accessible microstates)
if T is high –> change in entropy for given flow of heat is less
how does entropy work with heat flow
heat flows into system, entropy in system goes up, entropy in surrounding goes down
3Rd law of thermodynamics
perfect crystal has zero entropy at absolute zero
S sys = 0 at 0 k
formula of third law
when would a crystal particle only have one microstate at absolute zero
when its perfect, a crystal has flawless alignemnt
explanation of third law of thermodynamics of the perfect crystal
a perfect crystal has flawless alignment of all particles, at absolute zero, the particles have minimum energy so theres only ONE MICROSTATE
What anchors the entropy scale to an ABSOLUTE VALUE
the microstate of a perfect crystal
perfect crystal has zero entropy at absolute zero
third law of thermodynamics
does enthalpy (H) have an absolute value
NO
whats the absolute value for entropy. why?
0
due to no entropy as a perfect crystal
adding heat to:
Lower T
less freedom of motion
fewer microstates
lower S
gives us:
Higher T
More freedom of motion
more microstates
higher S
all 3 laws of thermodynamics shortened
- total energy remains constant
- total energy of the universe increases
- a perfect crystal has zero entropy at absolute zero
Formulas for all 3 laws
- ΔE sys + ΔE surr = ΔE univ = 0
- ΔS univ = ΔS sys + ΔS surr >0
- S sys = 0 at 0K
STANDARD MOLAR ENTROPY (S°)
entropy of 1 mole of substance in standard condition
standard molar entropies are _______ _____ measured against an ________ ________ point (perfect order)
absolute entropies
absolute reference
Standard entropy of rxn (ΔS° rxn) is the entropy change that occurs when
all reactants and products are in their standard states
Entropy is a state function and is _______
extensive
ΔS°rxn = S°(products) - S° (reactants)
standard entropy of reaction equation
aA + bB —> cC + dD in a generalized reaction turns into
ΔS°rxn = [cS°(c) + dS°(D)] - [aΔS(A) + bS°(B)]
Second law can be reframed to
in the system alone so
spontaneous reactions proceed to the direction that increases the entropy of the system
SPONTANEOUS PROCESS
must be favored by ____ in ethalpy
must be favored by _____ in entropy
decrease (-ΔH rxn)
increase (+ΔS rxn)
Gibbs free energy change (ΔG) evaluates spontaneity as
a function of enthalpy and and entropy OF THE SYSTEM ALONE
ΔG sys = ΔH sys - TΔS sys
gibbs free energy formula
ΔG < 0
process is spontaneous
ΔG = 0
system at equilibrium
ΔG > 0
process is non-spontaneous
what does lowering free energy do for chemical reactions
its the driving force
- ΔH sys and +ΔS sys favour
spontaneity
Entropic contribution to free energy change (-TΔS) is increasingly important at
higher temps
ΔG is the MAXIMUM ______ _____ that can be done by a system as it undergoes spontaneous process at constant temp and pressure: (formula)
useful work
ΔG= wmax
ΔG is also _________ work that must be done on a system to ____ the occurence of a non-spontaneous process
minimum
drive
standard free energy change (ΔG° or ΔG°rxn) is…
gibbs free energy change that occurs when all reactants and products are in their standard states
ΔG°f is
standard free energy of formation of a compound in its standard state from its component elements in THEIR standard states
ΔG°f rxn = (equation)
ΔG°f (products) - ΔG°f (reactants)
ΔG°f of an element in standard state is
zero
ΔG also tells us whether a reaction will/wont
proceed
ΔH > 0 and ΔS <0, its
if ΔH > 0 and ΔS > 0, its spontaneous only at
NEVER spontaneous
spontaneous at high temps
if ΔH < 0 and ΔS <0, its
spontaneous at low temps
if ΔH < 0 and ΔS>0, its
ALWAYS spontaneous
waht does ΔG = ΔG° + RTln1/K tell us
calculate ΔG under any set of conditions
ΔG < 0, ln (Q/K) < 0
ΔG = 0, ln(Q/K) =0
ΔG > 0, ln (Q/K) > 0
process proceeds (forward) spontaneously
Process is at equilibrium
Reverse proceeds proceeds spontaneously
A PICTURE WITH POSITIVE ΔG° will go from
low to high
a picure with a NEGATIVE ΔG° will go from
high to low
For a reaction with ΔG° > 0, and 100% reactants, products will be formed until
ΔG = 0
if ΔG° < 0 and Q =K, then
no net change in products/reactants
for reaction mixtures with Q > K what must be true
reactants must be formed
can Q be predicrted from ΔG°
no
waht can Q be predictd from
inital conidtions
when is ΔG° = ΔG
when all standard conditions are met
partial pressures are at 1atm
all concetrations at 1M
Q <1
Q > 1
ΔG IS NEGATIVE
ΔG° IS POSITIVE
ΔGrxn < 0
ΔGrxn > 0
ALWAYS spont
always non spont
