Thermodynamics Flashcards by elim yang

What is a spontaneous change?

A change that happens on its own, without the need of energy from outside the system. (theres an exception)

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Whats the exception to the “concept” of energy free spontaneous change?

sometimes activation energy is required to initiate a spontaneous change

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If a change is ——- in one direction, it will be ———– in the reverse direction

spontaneous

non-spontaneous

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non-spontaneous reactions and processes may be ______ with……..

driven

continual input of energy

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Many exothermic processes are……

spontaneous

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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.

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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

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Dissolution and ice melting is usually what type of transformation

endothermic

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what does an increase in freedom of motion of particles in a system indicate

more space to move so favoring spontaneity

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The measure of energy dispersal and freedom of motion in a system is called

entropy

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unit denoted for entropy

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Positive ΔS indicates

increased dispersal (of energy)

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Negative ΔS indicates

decreased dispersal (of energy)

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whats a life hack way to think about entropy

more entropy = MORE RANDOMNESS

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ΔS formula

Sfinal - S inital

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ΔS unit

J/K

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S° (standard molar entropy)

entropy of 1 mole of the pure substance in its standard state

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Entropy is correlation with bond ______ in STATES

tightness

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solid STATE has ______ bond so entropy is ______

tighter

less

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but don’t confuse tighter bonds as more molecules.

More molecules means

more entropy

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“more energy disperse = more entropy” is waht

when more molecules have higher entropy than less molecules

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More flexible and complex chemicals means

more entropy

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what is the dominating effect of molecular complexity

the physical state

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When does the complexity and flexibility of chemicals hold true (only 1 scenario)

WHEN SUBSTANCES ARE IN THE SAME STATE

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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

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

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

1. total energy remains constant 2. total energy of the universe increases 3. a perfect crystal has zero entropy at absolute zero

Formulas for all 3 laws

1. ΔE sys + ΔE surr = ΔE univ = 0 2. ΔS univ = ΔS sys + ΔS surr >0 3. 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 = [**c**S°(c) + **d**S°(D)] - [**a**ΔS(A) + **b**S°(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°

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