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CHM135 > Thermodynamics > Flashcards

Thermodynamics Flashcards

1
Q

What is a spontaneous change?

A

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

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2
Q

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

A

sometimes activation energy is required to initiate a spontaneous change

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3
Q

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

A

spontaneous

non-spontaneous

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4
Q

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

A

driven

continual input of energy

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5
Q

Many exothermic processes are……

A

spontaneous

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6
Q

are instant ice pack reactions exo or endo? are they spontaneous?

A

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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7
Q

Is ice melting exo or endo? is it spontaneous?

A

it is endo as heat is being absorbed into the ice cube.

yes it is spontaneous

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8
Q

Dissolution and ice melting is usually what type of transformation

A

endothermic

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9
Q

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

A

more space to move so favoring spontaneity

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10
Q

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

A

entropy

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11
Q

unit denoted for entropy

A

S

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12
Q

Positive ΔS indicates

A

increased dispersal (of energy)

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13
Q

Negative ΔS indicates

A

decreased dispersal (of energy)

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14
Q

whats a life hack way to think about entropy

A

more entropy = MORE RANDOMNESS

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15
Q

ΔS formula

A

Sfinal - S inital

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16
Q

ΔS unit

A

J/K

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17
Q

S° (standard molar entropy)

A

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

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18
Q

Entropy is correlation with bond ______ in STATES

A

tightness

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19
Q

solid STATE has ______ bond so entropy is ______

A

tighter

less

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20
Q

but don’t confuse tighter bonds as more molecules.

More molecules means

A

more entropy

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21
Q

“more energy disperse = more entropy” is waht

A

when more molecules have higher entropy than less molecules

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22
Q

More flexible and complex chemicals means

A

more entropy

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23
Q

what is the dominating effect of molecular complexity

A

the physical state

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24
Q

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

A

WHEN SUBSTANCES ARE IN THE SAME STATE

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25
Q

s < l < g which way does entropy arrow point

A

right

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26
Q

As temperature increases, entropy will also

A

increase

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27
Q

are jumps for states due to temperature on a graph continuous

A

no they are discontinous

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28
Q

the cyclic forms of molecules are closed off and rigid, so they are…… (2 diff sayings)

A

conformationally restricted

entropically disfavored

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29
Q

Does salt gain or lose entropy when dispersed

A

gain

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30
Q

Does water gain or lose entropy when dissolving something, why?

A

loses entropy as its ordered around the ions

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31
Q

Net entropy change depends on what

A

relative magnitudes of entropy changes in both solute and solvent entropy

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32
Q

Why does increased entropy favour spontaneous change

A

High entropy configurations can be achieved in more ways than low entropy configurations so its more likely to occur

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33
Q

Absolute entropies can be calculated from # of ________

A

microstates

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34
Q

Spontaneity seems to be promoted by an ________ in __________

A

increase

entropy

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35
Q

Does the sign of ΔS for a system’s transformation predict the direction of a spontaneous reaction

A

NO

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36
Q

example of why spontaneity can not be predicted by the sign alone

A

Ice melts SPONTANEOUSLY at high temps

water freezes SPONTANEOUSLY at low temps

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37
Q

FIRST law of thermodynamics

A

the energy in the universe remains constant

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38
Q

SECOND law of thermodynamics

A

Spontaneous reactions proceed in the direction that INCREASES the entropy of the universe

39
Q

ΔS univ = ΔS sys + Δsurr > 0

this is what

A

second law of thermodynamics formula

40
Q

any decrease in the entropy of the system must be OFFSET by what so that the process remains spontaenous

A

larger increase in entropy of surroundings for that process to remain spontaneous

41
Q

2nd law’s implications (2)

A

isolated systems always evolve toward higher-entropy states

the energy of the universe is always increasing

42
Q

What concepts does the 2nd law link together

A

heat flow and temperature

43
Q

how is temperature and heat flow linked (something to do with the AMOUNT of change in entropy)

A

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

44
Q

how does entropy work with heat flow

A

heat flows into system, entropy in system goes up, entropy in surrounding goes down

45
Q

3Rd law of thermodynamics

A

perfect crystal has zero entropy at absolute zero

46
Q

S sys = 0 at 0 k

A

formula of third law

47
Q

when would a crystal particle only have one microstate at absolute zero

A

when its perfect, a crystal has flawless alignemnt

47
Q

explanation of third law of thermodynamics of the perfect crystal

A

a perfect crystal has flawless alignment of all particles, at absolute zero, the particles have minimum energy so theres only ONE MICROSTATE

48
Q

What anchors the entropy scale to an ABSOLUTE VALUE

A

the microstate of a perfect crystal

49
Q

perfect crystal has zero entropy at absolute zero

A

third law of thermodynamics

50
Q

does enthalpy (H) have an absolute value

A

NO

51
Q

whats the absolute value for entropy. why?

A

0

due to no entropy as a perfect crystal

52
Q

adding heat to:

Lower T

less freedom of motion

fewer microstates

lower S

gives us:

A

Higher T

More freedom of motion

more microstates

higher S

53
Q

all 3 laws of thermodynamics shortened

A
  1. total energy remains constant
  2. total energy of the universe increases
  3. a perfect crystal has zero entropy at absolute zero
54
Q

Formulas for all 3 laws

A
  1. ΔE sys + ΔE surr = ΔE univ = 0
  2. ΔS univ = ΔS sys + ΔS surr >0
  3. S sys = 0 at 0K
55
Q

STANDARD MOLAR ENTROPY (S°)

A

entropy of 1 mole of substance in standard condition

56
Q

standard molar entropies are _______ _____ measured against an ________ ________ point (perfect order)

A

absolute entropies

absolute reference

57
Q

Standard entropy of rxn (ΔS° rxn) is the entropy change that occurs when

A

all reactants and products are in their standard states

58
Q

Entropy is a state function and is _______

A

extensive

59
Q

ΔS°rxn = S°(products) - S° (reactants)

A

standard entropy of reaction equation

60
Q

aA + bB —> cC + dD in a generalized reaction turns into

A

ΔS°rxn = [cS°(c) + dS°(D)] - [aΔS(A) + bS°(B)]

61
Q

Second law can be reframed to

A

in the system alone so

spontaneous reactions proceed to the direction that increases the entropy of the system

62
Q

SPONTANEOUS PROCESS

must be favored by ____ in ethalpy

must be favored by _____ in entropy

A

decrease (-ΔH rxn)
increase (+ΔS rxn)

63
Q

Gibbs free energy change (ΔG) evaluates spontaneity as

A

a function of enthalpy and and entropy OF THE SYSTEM ALONE

64
Q

ΔG sys = ΔH sys - TΔS sys

A

gibbs free energy formula

65
Q

ΔG < 0

A

process is spontaneous

66
Q

ΔG = 0

A

system at equilibrium

67
Q

ΔG > 0

A

process is non-spontaneous

68
Q

what does lowering free energy do for chemical reactions

A

its the driving force

69
Q
  • ΔH sys and +ΔS sys favour
A

spontaneity

70
Q

Entropic contribution to free energy change (-TΔS) is increasingly important at

A

higher temps

71
Q

ΔG is the MAXIMUM ______ _____ that can be done by a system as it undergoes spontaneous process at constant temp and pressure: (formula)

A

useful work

ΔG= wmax

72
Q

ΔG is also _________ work that must be done on a system to ____ the occurence of a non-spontaneous process

A

minimum

drive

73
Q

standard free energy change (ΔG° or ΔG°rxn) is…

A

gibbs free energy change that occurs when all reactants and products are in their standard states

74
Q

ΔG°f is

A

standard free energy of formation of a compound in its standard state from its component elements in THEIR standard states

75
Q

ΔG°f rxn = (equation)

A

ΔG°f (products) - ΔG°f (reactants)

76
Q

ΔG°f of an element in standard state is

A

zero

77
Q

ΔG also tells us whether a reaction will/wont

A

proceed

78
Q

ΔH > 0 and ΔS <0, its

if ΔH > 0 and ΔS > 0, its spontaneous only at

A

NEVER spontaneous

spontaneous at high temps

79
Q

if ΔH < 0 and ΔS <0, its

A

spontaneous at low temps

80
Q

if ΔH < 0 and ΔS>0, its

A

ALWAYS spontaneous

81
Q

waht does ΔG = ΔG° + RTln1/K tell us

A

calculate ΔG under any set of conditions

82
Q

ΔG < 0, ln (Q/K) < 0

ΔG = 0, ln(Q/K) =0

ΔG > 0, ln (Q/K) > 0

A

process proceeds (forward) spontaneously

Process is at equilibrium

Reverse proceeds proceeds spontaneously

83
Q

A PICTURE WITH POSITIVE ΔG° will go from

A

low to high

84
Q

a picure with a NEGATIVE ΔG° will go from

A

high to low

85
Q

For a reaction with ΔG° > 0, and 100% reactants, products will be formed until

A

ΔG = 0

86
Q
A
87
Q

if ΔG° < 0 and Q =K, then

A

no net change in products/reactants

88
Q

for reaction mixtures with Q > K what must be true

A

reactants must be formed

89
Q

can Q be predicrted from ΔG°

A

no

90
Q

waht can Q be predictd from

A

inital conidtions

91
Q

when is ΔG° = ΔG

A

when all standard conditions are met

partial pressures are at 1atm

all concetrations at 1M

92
Q

Q <1

Q > 1

A

ΔG IS NEGATIVE

ΔG° IS POSITIVE

93
Q

ΔGrxn < 0

ΔGrxn > 0

A

ALWAYS spont

always non spont

CHM135 (8 decks)

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