chapter 16: spontaneous entropy Flashcards
what is the first law of thermodynamics
- energy cannot be created or destroyed
- total energy of the Universe is constant
- 3. energy can be transferred
what is the equation for
Euniverse
Euniverse= 0= Esystem + Esurroundings
what is internal energy
the total energy in a system ( kinetic + potential)
what is a spontaneous process?
a process that can proceed without any outside energy ( proceed on its own)
what is a nonspontaneous process
- requires energy to proceed
if something is spontaneous in one direction, what will happen in the other direction?
if something is spontaneous in one direction then it will be nonspontaneous in the other direction
what is an example of of a spontaneous process
nail rusting
what is the spontaneous and nonspontaneous of melting and freezing in ice
- above 0 degrees is spontaneous to melt
- below 0 is spont. for ice to form
does rate or speed affect spontaneity
no, a process can be spontaneous and slow
what is the difference between thermodynamics and kinetics
- thermodynamics tells us the DIRECTION and EXTENT of the rxn
- Kinetics tells us the speed of the reaction
when a piece of metal is heated to 150 degrees and added to water and the water gets hotter is that spontaneous or nonspontaneous
that is spontaneous because heat is flowing from high to low ( meaning no energy input)
if a decompose H2O into H2 and O2
that is a nonspontaneus process because it takes energy to break them apart
endothermic does not equal
nonspontaneous
most spontaneous processes are what
exothermic but some are endothermic
what are the two factors that are involved in spontaneous processes
- decrease in the energy (enthalpy)
- @ a constant temp, an increase in the disorder of a system ( entropy)
what is the symbol for entropy
S
what is entropy
the amount of randomness or disorder in a system or the increase of the ways to rearrange the components
what is the entropy formula
S = k ln(W)
- k = 1.38x^-23
W = the number of ways to arrange the components
what happens to S when W increases
S also increases
what are some examples of a macrostate
P,V,T
what is a microstate
number of different possible arrangements of molecular position and kinetic energy at a particular thermodynamic stat
what is the relationship between entropy and microstates
entropy increases = # of microstates increases
what is the second law of thermo
- any spont process, the entropy of the universe increases (Suniv >0)
- entropy is NOT conserved
- systems proceed to increase the entropy of the univ
what causes an increase in entropy
- increase in temp
- increase in moving molecules
- increase in volume
what does the change in entropy depend on
the initial and final states of the system
S= Sfinal -Sinitial
how does temp increase cause an increase in entropy
increase in temp = increase in speed of moving particles = greater KE= microstates increase
will a increase in temp have a wider or skinner graph
wider graph
how does greater volume increase with entropy
greater volume = more number of positions for molecules to occupy
how does entropy increase with phase changes
more freedom of motion= increase in entropy
Solids < liquid
what is translational motion
whole atom or molecule changes its location in 3d space
what is rotational motion
whole molecule spins around an axis in 3D space
what is vibratinoal motion and what are the subtypes of vibrational motion
motion chat changes only the shape of the molecule
1, stretching, bending, internal rotation
when will entropy of a system also increase again
- perform endothermic PHASE change
- dissolve salt with lowly charged ions
- # of moles increases during a chemical rxn
what has more motion an atomic or a molecule and what can’t atoms do
a molecule
atoms can’t rotate
what is the equation for the System
qrev/T
what is the difference between reversible and irreversible
- irreversible cannot be undone
- reversible can be undone
what processes are isothermal
melting and vaporization
what is qrev/T equivalent to
nHfus/ T
what are the SI units for Ssystem
J/K
what is the equation for Sunive
Syst + Surr = Suniv
what does Ssurr depend on
how much heat is absorbed or given
if Hsys is negative then what happens to the entropy of Surr
the entropy of the surroundings increases
what is the equation for Suniv when its a reversible process
Suniv = System + surrounds= 0
what is the equation for a irrevesible process for Suniv
Suniv = system + surr > 0
sys (+)
surr (+)
Suniv (+)
is it spontaneous or not
it is spontaneous
sys -
surr = -
univ = -
the reaction is not spontaneous in the forward but spontaneous in the reverse
sys = +
surr = -
univ =/
yes spontaneous if the system is larger than the surrounding
sys = - surr = + univ = ?
yes, if the surr is larger than the sys
what 2 factors are involved in spontaneous processes
- decrease in energy of the system
- @ a constant temp, increase in the amount of disorder
if H>0 what will the spontaneity be
- endothermic
- spontaneous of S is > 0 2 certain temps
if H<0 what is the spontaneity
- process is exothermic
- if S <0 then it is nonspon. at certain temps
heat is exiting the system
what is Gibbs free energy and the equation
- invented by american J gibbs
- G = H-TS
- free energy
What is the gibbs free energy equation for processes occurring at a constant temp
G = H-T (change in S)
what is the relationship between spontaneity with G and S
S >0 and G<0 then the reaction is spontaneous
if G <0 then what direction
spontaneous in the forward direction; product favored
if G =0
at equilibrium
g>0
reaction is nonspontaneous in the forward direction, aka react. favored
why is G preferred over Suniv
because G only depends on the system and avoids the complications of the surroundings
in the equation for free enerfy what represents the enthalpy and the entropy
delta H = enthalpy ( can be + or -)
-Tdelta (s) = entropy ( s can be positive or negative)
if H<0 and S>0 what does it mean
rxn is spontaneous at all temps
* if S<0 then the rxn is only spontaneous at low temps
if H>0 and S<0 then what does it mean
rxn is nonspontaneous at all temps
* if S>0 the rxn is only nonspontaneous at low temps
what is the heat capacity
the amount of energy required to raise the temp of a substance by 1 K
what is the third law of thermodyamics
- decrease the thermal energy = motional energy decreases
- less energy is stored, entropy decreases
- temp increased, atoms gain vibrational motion
what does the 3rd law of thermo say about the entropy of a pure crystalline
@ abs 0 is 0
what increases the standard molar entropies
- generally increase w/ increasing molar mass
- increase w/ the number of atoms
how to calculate Hrxn
nProducts - nReactants
what does the degree symbol mean on Gibbs free energy equation?
- standard conditions
when does Delta G = 0
elements that are in their standard states
ex. H2, O2, n2
what rules do tou apply to delta G that are like hess’s law
- muliply by some factor, then Grxn is also multiplied by the same factor
- flipped (change the sign of the Grxn)
how can a nonspontaneous reaction be made spontaneous
by coupling it with another process that is highly spontaneous
how does Delta G relate to Delta G (degrees)
- as volume increases= microstates increases= decrease in pressure
- for real reactions that are not under nonstandard conditions
G = G + RT ln Q
- R = 8.314J/mol.K
Q= prod/react
what is G equation at equilibrium
K = e^-G/RT
how is work and free energy related to free energy
max work is equal to the change in free energy
Wmax= G
- nonspontaneous = minium amount of work
- spontaneous = energy that is free to do useful work
