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chemistry 1102 > chapter 16: spontaneous entropy > Flashcards

chapter 16: spontaneous entropy Flashcards

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1
Q

what is the first law of thermodynamics?

A

energy cannot be created or destoryed

  • total energy of the univ. is constant
  • energy can be transferred
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2
Q

what is the formula for the first law of thermodynamcis

A

deltaE(universe) = 0 = delta E(system) + deltaE(surroundings)

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3
Q

what is the internal energy

A

total energy possessed by a system

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4
Q

what is a spontaneous process

A

a process capable of proceeding in a given direction without needing to driven by an outside source of energy

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5
Q

what is a nonspontaneous reaction

A

requires energy input to proceed

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6
Q

processes that are spontaneous in one direction are nonspontaneous in what direction?

A

the opposite direction

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7
Q

what is an example of a spontaneous reaction

A

iron in nail reacting with oxygen in the air to form iron oxide

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8
Q

what temperature is spontaneous for ice to melt

A

above 0 degrees

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9
Q

what temperature is it spontaneous for ice to form

A

below 0 degrees

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10
Q

is a process is spontaneous does it mean it’s fast

A

no it doesn’t mean it is fast

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11
Q

which process is fast

A

acid-base neutralization

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12
Q

what can thermodynamics tells us?

A

the direction and extent of the reaction

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13
Q

what does kinetics tell us?

A

the speed of a reaction

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14
Q

endothermic does not equal what

A

nonspontaneous

  • most spontaneous processes are exothermic but some are endothermic
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15
Q

what is entropy

A

amount of disorder or randomness in a system

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16
Q

what two factors are involved in spontaneous processes

A
  • decrease in enthalpy
  • @ a constant temp, an increase in the amount of entropy
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17
Q

what causes entropy to increase

A

increases with the number of energetically equivalent ways to arrange the components of a system to achieve a particular state

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18
Q

what did autrian physicist ludwig boltzamann do

A

expressed entropy as

S= k ln(W)

  • k is the boltzmann constant
  • W is the number of energetically equivalent ways to arrange the components
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19
Q

what is the boltzmann constant

A

k = 1.38 x 10^23

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20
Q

what happens to S as W increases in the equation S = k ln (W)

A

as W increases do does S because W is the different ways the particles can be rearranged

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21
Q

what has to remain constant for the overall energy to remain constant

A

temperature, volume, pressure and moles

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22
Q

what happens to the energy in particles as they collide with one another or the walls

A

they lose energy

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23
Q

what is a microstate

A

it is a detailed look at the energy that molecules or other particles have.

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24
Q

when does entropy increase

A

with the number of microstates

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25
Q

what is the second law of thermodynamics

A

states that when energy is transferred or transformed it becomes wasted

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26
Q

what microstates cause entropy to increase while it increases

A
  • temp
  • volume
  • number of independently moving molecules
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27
Q

an increase in temperature increases what

A
  • avg speed of molecules
  • microstates increase
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28
Q

how does greater volume increase the number of microstates

A

greater positions for the molecules to occupy

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29
Q

an increase in entropy is the same as what

A
  • increase in randomness or disorder of a system
  • increased dispersion of energy ( spreading out of energy)
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30
Q

as the freedom of motion of moleucles increases what happens to entropy

A

it increases

-example: as ice melts( goes from a solid to liquid) it gains more freedom of motion

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31
Q

what happens to the motion of molecules when a substance is heated

A

the motion of molecules increases

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32
Q

what is the average KE of the molecules of an ideal gas proportional to

A

its absolute temperature

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33
Q

what are the 3 kinds of motion molecules can undergo

A
  • transitional
  • rotational
  • vibrational
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34
Q

what is translational motion

A

when the whole atom or molecule changes its location in 3D space

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35
Q

what is rotational motion

A

when the whole molecule spins around an axis in 3D space

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36
Q

what is vibrational motion

A

motion that changes only the shape of a molecule (motion of a molecule)

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37
Q

what are the types of vibrational motion

A
  • stretching
  • bending
  • internal rotation
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38
Q

which type of motion contributes the most to the entropy of a substance?

A

translational

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39
Q

what is the symbol for heat

A

q

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40
Q

an increase in temperature means what heat

A

then heat increases

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41
Q

which type of motion is the cause of collisions

A

translational

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42
Q

which type of motion influences the orientation for an effective collision

A

rotational

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43
Q

different physical states have what types of entropy

A

different types of entropy

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44
Q

what mode of motion can gas molecules do

A

translation

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45
Q

what modes of motion can a gas molecule do

A
  • translation
  • rotation
  • vibration
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46
Q

what can’t atoms do

A

rotate or vibrate

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47
Q

what modes of motion can a liquid atom do

A

translation

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48
Q

what modes of translation can liquid molecules do

A

translation, rotation, vibration

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49
Q

what modes of motion can solid atoms do

A

vibrate

50
Q

what modes of motion can a solid molecule do

A

vibration

51
Q

why can solid atoms and moleucles vibrate

A
  • they have a different type of vibration that is twitching vibrations
52
Q

what happens when an ionic solid is dissolved in water

A

it dissociates into ions

53
Q

which has more freedom of motion the ions or the water molecules

A

ions

54
Q

how are the dissolved ions free to move around

A

water molecules encapsulate them and act as their transport partners

55
Q

what happens to entropy from the water’s perspective

A

they have a decrease in entropy and have less freedom of motion because increasing the solute means that there is less space for the water molecules

56
Q

what happens in this reaction when you form the new N-O bonds?

2NO(g) + O2 = 2NO (g)

A
  • entropy decreases and the degrees of freedom decreases
  • few microstates and the entropy is lower (moving from 3 moles to 2 moles)
57
Q

when does the entropy of a system increase in a reaction

A
  • perform an endothermic phase change ( solid to gas, liquid to gas)
  • dissolve salt with lowly charged ions
  • # of moles increases during a chemical reaction
58
Q

what is the standard pressure and temperature for stp conditions

A
  • 298 kelvin
  • 1 atm
59
Q

what is the symbol for entropy

A

Delta S

60
Q

on a macroscopic scale what is the chang in entropy equal to

A

the heat that would be transferred in a reversible process / temperature

61
Q

what is the equation for the change in entropy and when do you use it

A

q(reversible) / T

  • use it for isothermal processes
62
Q

what does isothermal mean

A

constant temp

63
Q

in a reversible process how can the system change

A

the sys and surr can be put back in their original states by reversing the process

64
Q

what work does a reversible change produce

A

the max amount of work that can be achieved by the system on the surrounding

Wrev = Wmax

65
Q

what is a irreversible process

A

cannot be undone by reversing the system

66
Q

what processes are irreversible

A

spontaneous process

67
Q

what phase changes are isothermal process

A

melting and vaporization

68
Q

what is the equation for delta S(system) for isothermal processes

A

nHfus / T

  • n = the number of moles
69
Q

what are the units for entropy

A

J/K

70
Q

why do you have to examine both the change in system and surroundings

A

entropy increases in a spontaneous reaction

so that means S(univ) is greater than 0 and entropy is not conserved so you have to look at both because they don’t cancel out

71
Q

what is the formula for change in universe

A

change in the system + the change in surroundings

72
Q

how can you distinguish between the change of system and surroundings

A

typically by in opposite signs

73
Q

what is the change in surrounding based on

A

how much heat is absorbed or given off by the surrondings

74
Q

what is the equation for change in surroundings

A
  • nH(fus)/ T
  • a process that emits heat to the surroundings increases the entropy of the surroundings
75
Q

what does it mean if S(universe) is greater than 0

A

the reaciton is spontaneous

76
Q

is the process spontaneous when S(sys), S(surr) and S(univ) is positive

A

yes

77
Q

what direction will the reaction proceed if S(univ) is less than 0

A

it will not proceed in the forward direction

78
Q

what is the spontaneity of negative system, surrounding, universe

A

not spontaneous ( occur in the opposite direction)

79
Q

what will happen if the system is + and the surroundings is -

A

spontaneous if system is larger than surroundings

80
Q

what will havppen if system is - and surroundings is +

A

yes, if the surronding has a larfer magnitude

81
Q

what is heat also referred to as

A

enthalpy

82
Q

what two factors are involed in a spontaneous process

A
  • decrease in enthalpy of the system

-@ a constant temp, increase in the entropy of a system

83
Q

what happens if delta H is > 0, and when will it be spontaneous

A

the process is endothermic and will be spontaneous if S >0 @ certain temps

84
Q

what happens if H <0 and what happens if S <0

A

the process is exothermic and usually spontaneous

  • S <0 then it is nonspontaneous
85
Q

who developed the relationship between ΔH and ΔS

A

J. willard gibbs

86
Q

what is the formula for gibbs energy

A

G = H – TS

  • T is absolute temperature
87
Q

what is the equation for gibbs when the process is at a constant temp

A

ΔG = ΔH – TΔS

88
Q

what is the equation that relates spontaneity to gibbs free enrgy

A

–TΔSuniv = ΔHsys – TΔSsys

  • G = -TΔSuniv at constant T and P
89
Q

if g<0 what does that indicate about the spontaneity

A

it is spontaneous ( moving in forward direction) (product favored)

  • S is also greater than 0
90
Q

what happens when ΔG = 0,

A

the reaction is at equilibrium

91
Q

what happens when f ΔG > 0

A

the reaction is nonspontaneous and is the backward direction (aka reactant favored)

  • work has to be applied from the surr for the reaction to occur
92
Q

why is G preferred of S(univ) to describe spontaneity

A

g only depends on the system and avoids the complications of the surroundings

93
Q

what does it mean when S >0

what does it mean when S<0

A

greater than 0 : increase in disorder

less than 0: decrease in disorder

94
Q

what happens if H is - and H is + at low temperature and high temp

A

the reaction is spontaneous

95
Q
A
96
Q

what happens if H and S have different signs

A

the spontaneity does not depend on the temperature

97
Q

what happens if H is positive and S is negative

what happens when s is positive

A

the reaction is nonspontaneous at all temps

  • the rxn is nonspont. at low temps
98
Q

what is heat capacity

A

the amount of energy needed to raise the temp of a substance

99
Q

what is the third law of thermodynamics

A
  • decrease thermal energy of the system by lowering temp, motional energy decreases
  • less energy stored, entropy decreases
  • entropy of a pure crystalline substance at absolute 0 is 0
  • temp increase = more vibrational motion
100
Q
A
101
Q

what are standard molar entropies

A

molar entropy values in their standard states

102
Q

how does the standard molar entropy increase

A
    • increasing molar mass
    • increase with the number of atoms
      • increasing the # of degrees of freedom
      • increasing the microstates
103
Q

what is the formula for standard enthalpy change

A

ΔH° rxn = Σn ΔHf °(products) − Σn ΔHf °(reactants)

104
Q

what is a standard state

A

substance in pure form

  • pure gas = 1 atm

pure solid or liquid = 1 atm and temp of 25 degrees

concentration = 1

105
Q

if you already know Hrxn and Srxn of can calculate them from Hf and S of the substance then what equation can you use

A

ΔG° rxn = ΔH° rxn – T ΔS° rxn

106
Q

how can you use hf to calculate Gibbs energy

A

the standard free energies of formation

107
Q

what is a state function

A

a property whose value does not depend on the path taken to reach that specific value

108
Q

what does Hess’s law say and how can that be applied to gibbs energy

A

if a rxn is carried out in steps gibbs for the overall rxn will equal the sum of the free energy changes for the individuals steps

  • multiplied by a factor then grxn is also multiplied
  • flipped (reversed and sign changes)
109
Q

how can you make a nonspontaneous reaction spontaneous

A

coupling it with another process that is highly spontaneous

110
Q

what do real rxns not achieve

A

the theoretical limit of available free energy

  • irreversible
  • −ΔG = ΔG° ONLY under standard conditions
111
Q

for real rxns when does the free energy change

A

as the reaction proceeds because it is dependent on the pressure of a gas or on the concentration of the species in the solution

112
Q

as volume increases what happens to the number of potential microstates

A

the microstates increase, and there is a decrease in pressure

113
Q

what is the equation for delta g under nonstandard conditions, what does R stand for and what does Q stand for

A

ΔG = ΔG° + RT ln Q

  • R is the ideal gas constant ( 8.314 J/K)
  • Q is the reaction quotient ( for standard conditions Q =1)
114
Q

what happens when q < k

A

excess reactants relative to products meaning the rxn proceeds in the forward direction

115
Q

when q>k

A

the rxn proceeds spontaneouslt in the reverse direction

116
Q

what is the maxium amount of work equal to

A

change in free energy

117
Q

what is the work for a nonspontaneous process

A

G is +, and represents the minimum amount of work

118
Q

for a spontaneous process what does the work look like

A

G is (-) and g represents the energy that is free to do useful work

119
Q

what happens in a real cyclic process in the system

A

work is changed to heat in the surroundings and the entropy of the universe increases

120
Q

what happens when energy is used to do work

A

it becomes less organized and concetrated so less useful

chemistry 1102 (6 decks)

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