chapter 16: spontaneous entropy Flashcards
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
2
Q
what is the formula for the first law of thermodynamcis
A
deltaE(universe) = 0 = delta E(system) + deltaE(surroundings)
3
Q
what is the internal energy
A
total energy possessed by a system
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
5
Q
what is a nonspontaneous reaction
A
requires energy input to proceed
6
Q
processes that are spontaneous in one direction are nonspontaneous in what direction?
A
the opposite direction
7
Q
what is an example of a spontaneous reaction
A
iron in nail reacting with oxygen in the air to form iron oxide
8
Q
what temperature is spontaneous for ice to melt
A
above 0 degrees
9
Q
what temperature is it spontaneous for ice to form
A
below 0 degrees
10
Q
is a process is spontaneous does it mean it’s fast
A
no it doesn’t mean it is fast
11
Q
which process is fast
A
acid-base neutralization
12
Q
what can thermodynamics tells us?
A
the direction and extent of the reaction
13
Q
what does kinetics tell us?
A
the speed of a reaction
14
Q
endothermic does not equal what
A
nonspontaneous
- most spontaneous processes are exothermic but some are endothermic
15
Q
what is entropy
A
amount of disorder or randomness in a system
16
Q
what two factors are involved in spontaneous processes
A
- decrease in enthalpy
- @ a constant temp, an increase in the amount of entropy
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
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
19
Q
what is the boltzmann constant
A
k = 1.38 x 10^23
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
21
Q
what has to remain constant for the overall energy to remain constant
A
temperature, volume, pressure and moles
22
Q
what happens to the energy in particles as they collide with one another or the walls
A
they lose energy
23
Q
what is a microstate
A
it is a detailed look at the energy that molecules or other particles have.
24
Q
when does entropy increase
A
with the number of microstates
25
what is the second law of thermodynamics
states that when energy is transferred or transformed it becomes wasted
26
what microstates cause entropy to increase while it increases
- temp
- volume
- number of independently moving molecules
27
an increase in temperature increases what
- avg speed of molecules
- microstates increase
28
how does greater volume increase the number of microstates
greater positions for the molecules to occupy
29
an increase in entropy is the same as what
- increase in randomness or disorder of a system
- increased dispersion of energy ( spreading out of energy)
30
as the freedom of motion of moleucles increases what happens to entropy
it increases
-example: as ice melts( goes from a solid to liquid) it gains more freedom of motion
31
what happens to the motion of molecules when a substance is heated
the motion of molecules increases
32
what is the average KE of the molecules of an ideal gas proportional to
its absolute temperature
33
what are the 3 kinds of motion molecules can undergo
- transitional
- rotational
- vibrational
34
what is translational motion
when the whole atom or molecule changes its location in 3D space
35
what is rotational motion
when the whole molecule spins around an axis in 3D space
36
what is vibrational motion
motion that changes only the shape of a molecule (motion of a molecule)
37
what are the types of vibrational motion
- stretching
- bending
- internal rotation
38
which type of motion contributes the most to the entropy of a substance?
translational
39
what is the symbol for heat
q
40
an increase in temperature means what heat
then heat increases
41
which type of motion is the cause of collisions
translational
42
which type of motion influences the orientation for an effective collision
rotational
43
different physical states have what types of entropy
different types of entropy
44
what mode of motion can gas molecules do
translation
45
what modes of motion can a gas [**molecule**](https://s3-us-west-2.amazonaws.com/courses-images-archive-read-only/wp-content/uploads/sites/222/2014/12/20104246/Figure_14_03_01.jpg) do
- translation
- rotation
- vibration
46
what can't atoms do
rotate or vibrate
47
what modes of motion can a liquid atom do
translation
48
what modes of translation can liquid molecules do
translation, rotation, vibration
49
what modes of motion can solid atoms do
vibrate
50
what modes of motion can a solid molecule do
vibration
51
why can solid atoms and moleucles vibrate
- they have a different type of vibration that is twitching vibrations
52
what happens when an ionic solid is dissolved in water
it dissociates into ions
53
which has more freedom of motion the ions or the water molecules
ions
54
how are the dissolved ions free to move around
water molecules encapsulate them and act as their transport partners
55
what happens to entropy from the water's perspective
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
what happens in this reaction when you form the new N-O bonds?
2NO(g) + O2 = 2NO (g)
- entropy decreases and the degrees of freedom decreases
- few microstates and the entropy is lower (moving from 3 moles to 2 moles)
57
when does the entropy of a system increase in a reaction
- 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
what is the standard pressure and temperature for stp conditions
- 298 kelvin
- 1 atm
59
what is the symbol for entropy
Delta S
60
on a macroscopic scale what is the chang in entropy equal to
the heat that would be transferred in a reversible process / temperature
61
what is the equation for the change in entropy and when do you use it
q(reversible) / T
- use it for isothermal processes
62
what does isothermal mean
constant temp
63
in a reversible process how can the system change
the sys and surr can be put back in their original states by reversing the process
64
what work does a reversible change produce
the max amount of work that can be achieved by the system on the surrounding
Wrev = Wmax
65
what is a irreversible process
cannot be undone by reversing the system
66
what processes are irreversible
spontaneous process
67
what phase changes are isothermal process
melting and vaporization
68
what is the equation for delta S(system) for isothermal processes
nHfus / T
- n = the number of moles
69
what are the units for entropy
J/K
70
why do you have to examine both the change in system and surroundings
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
what is the formula for change in universe
change in the system + the change in surroundings
72
how can you distinguish between the change of system and surroundings
typically by in opposite signs
73
what is the change in surrounding based on
how much heat is absorbed or given off by the surrondings
74
what is the equation for change in surroundings
- nH(fus)/ T
- a process that emits heat to the surroundings increases the entropy of the **surroundings**
75
what does it mean if S(universe) is greater than 0
the reaciton is spontaneous
76
is the process spontaneous when S(sys), S(surr) and S(univ) is positive
yes
77
what direction will the reaction proceed if S(univ) is less than 0
it will not proceed in the forward direction
78
what is the spontaneity of negative system, surrounding, universe
not spontaneous ( occur in the opposite direction)
79
what will happen if the system is + and the surroundings is -
spontaneous if system is larger than surroundings
80
what will havppen if system is - and surroundings is +
yes, if the surronding has a larfer magnitude
81
what is heat also referred to as
enthalpy
82
what two factors are involed in a spontaneous process
- decrease in enthalpy of the **system**
**-**@ a constant temp, increase in the entropy of a system
83
what happens if delta H is \> 0, and when will it be spontaneous
the process is endothermic and will be spontaneous if S \>0 @ certain temps
84
what happens if H \<0 and what happens if S \<0
the process is exothermic and usually spontaneous
- S \<0 then it is nonspontaneous
85
who developed the relationship between ΔH and ΔS
J. willard gibbs
86
what is the formula for gibbs energy
G = H – TS
- T is absolute temperature
87
what is the equation for gibbs when the process is at a constant temp
ΔG = ΔH – TΔS
88
what is the equation that relates spontaneity to gibbs free enrgy
–TΔSuniv = ΔHsys – TΔSsys
- G = -TΔSuniv at constant T and P
89
if g\<0 what does that indicate about the spontaneity
it is spontaneous ( moving in forward direction) (product favored)
- S is also greater than 0
90
what happens when ΔG = 0,
the reaction is at equilibrium
91
what happens when f ΔG \> 0
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
why is G preferred of S(univ) to describe spontaneity
g only depends on the system and avoids the complications of the surroundings
93
what does it mean when S \>0
what does it mean when S\<0
greater than 0 : increase in disorder
less than 0: decrease in disorder
94
what happens if H is - and H is + at low temperature and high temp
the reaction is spontaneous
95
96
what happens if H and S have different signs
the spontaneity does not depend on the temperature
97
what happens if H is positive and S is negative
what happens when s is positive
the reaction is nonspontaneous at all temps
- the rxn is nonspont. at low temps
98
what is heat capacity
the amount of energy needed to raise the temp of a substance
99
what is the third law of thermodynamics
- 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
101
what are standard molar entropies
molar entropy values in their standard states
102
how does the standard molar entropy increase
* - increasing molar mass
* - increase with the number of atoms
* increasing the # of degrees of freedom
* increasing the microstates
103
what is the formula for standard enthalpy change
ΔH° rxn = Σn ΔHf °(products) − Σn ΔHf °(reactants)
104
what is a standard state
substance in pure form
- pure gas = 1 atm
pure solid or liquid = 1 atm and temp of 25 degrees
concentration = 1
105
if you already know Hrxn and Srxn of can calculate them from Hf and S of the substance then what equation can you use
ΔG° rxn = ΔH° rxn – T ΔS° rxn
106
how can you use hf to calculate Gibbs energy
the standard free energies of formation
107
what is a state function
a property whose value does not depend on the path taken to reach that specific value
108
what does Hess's law say and how can that be applied to gibbs energy
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
how can you make a nonspontaneous reaction spontaneous
coupling it with another process that is highly spontaneous
110
what do real rxns not achieve
the theoretical limit of available free energy
- irreversible
- −ΔG = ΔG° ONLY under standard conditions
111
for real rxns when does the free energy change
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
as volume increases what happens to the number of potential microstates
the microstates increase, and there is a decrease in pressure
113
what is the equation for delta g under nonstandard conditions, what does R stand for and what does Q stand for
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
what happens when q \< k
excess reactants relative to products meaning the rxn proceeds in the forward direction
115
when q\>k
the rxn proceeds spontaneouslt in the reverse direction
116
what is the maxium amount of work equal to
change in free energy
117
what is the work for a nonspontaneous process
G is +, and represents the minimum amount of work
118
for a spontaneous process what does the work look like
G is (-) and g represents the energy that is free to do useful work
119
what happens in a real cyclic process in the system
work is changed to heat in the surroundings and the entropy of the universe increases
120
what happens when energy is used to do work
it becomes less organized and concetrated so less useful
