chapter 16: spontaneous entropy Flashcards
what is the first law of thermodynamics?
energy cannot be created or destoryed
- total energy of the univ. is constant
- energy can be transferred
what is the formula for the first law of thermodynamcis
deltaE(universe) = 0 = delta E(system) + deltaE(surroundings)
what is the internal energy
total energy possessed by a system
what is a spontaneous process
a process capable of proceeding in a given direction without needing to driven by an outside source of energy
what is a nonspontaneous reaction
requires energy input to proceed
processes that are spontaneous in one direction are nonspontaneous in what direction?
the opposite direction
what is an example of a spontaneous reaction
iron in nail reacting with oxygen in the air to form iron oxide
what temperature is spontaneous for ice to melt
above 0 degrees
what temperature is it spontaneous for ice to form
below 0 degrees
is a process is spontaneous does it mean it’s fast
no it doesn’t mean it is fast
which process is fast
acid-base neutralization
what can thermodynamics tells us?
the direction and extent of the reaction
what does kinetics tell us?
the speed of a reaction
endothermic does not equal what
nonspontaneous
- most spontaneous processes are exothermic but some are endothermic
what is entropy
amount of disorder or randomness in a system
what two factors are involved in spontaneous processes
- decrease in enthalpy
- @ a constant temp, an increase in the amount of entropy
what causes entropy to increase
increases with the number of energetically equivalent ways to arrange the components of a system to achieve a particular state
what did autrian physicist ludwig boltzamann do
expressed entropy as
S= k ln(W)
- k is the boltzmann constant
- W is the number of energetically equivalent ways to arrange the components
what is the boltzmann constant
k = 1.38 x 10^23
what happens to S as W increases in the equation S = k ln (W)
as W increases do does S because W is the different ways the particles can be rearranged
what has to remain constant for the overall energy to remain constant
temperature, volume, pressure and moles
what happens to the energy in particles as they collide with one another or the walls
they lose energy
what is a microstate
it is a detailed look at the energy that molecules or other particles have.
when does entropy increase
with the number of microstates
what is the second law of thermodynamics
states that when energy is transferred or transformed it becomes wasted
what microstates cause entropy to increase while it increases
- temp
- volume
- number of independently moving molecules
an increase in temperature increases what
- avg speed of molecules
- microstates increase
how does greater volume increase the number of microstates
greater positions for the molecules to occupy
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)
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
what happens to the motion of molecules when a substance is heated
the motion of molecules increases
what is the average KE of the molecules of an ideal gas proportional to
its absolute temperature
what are the 3 kinds of motion molecules can undergo
- transitional
- rotational
- vibrational
what is translational motion
when the whole atom or molecule changes its location in 3D space
what is rotational motion
when the whole molecule spins around an axis in 3D space
what is vibrational motion
motion that changes only the shape of a molecule (motion of a molecule)
what are the types of vibrational motion
- stretching
- bending
- internal rotation
which type of motion contributes the most to the entropy of a substance?
translational
what is the symbol for heat
q
an increase in temperature means what heat
then heat increases
which type of motion is the cause of collisions
translational
which type of motion influences the orientation for an effective collision
rotational
different physical states have what types of entropy
different types of entropy
what mode of motion can gas molecules do
translation
what can’t atoms do
rotate or vibrate
what modes of motion can a liquid atom do
translation
what modes of translation can liquid molecules do
translation, rotation, vibration
what modes of motion can solid atoms do
vibrate
what modes of motion can a solid molecule do
vibration
why can solid atoms and moleucles vibrate
- they have a different type of vibration that is twitching vibrations
what happens when an ionic solid is dissolved in water
it dissociates into ions
which has more freedom of motion the ions or the water molecules
ions
how are the dissolved ions free to move around
water molecules encapsulate them and act as their transport partners
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
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)
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
what is the standard pressure and temperature for stp conditions
- 298 kelvin
- 1 atm
what is the symbol for entropy
Delta S
on a macroscopic scale what is the chang in entropy equal to
the heat that would be transferred in a reversible process / temperature
what is the equation for the change in entropy and when do you use it
q(reversible) / T
- use it for isothermal processes
what does isothermal mean
constant temp
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
what work does a reversible change produce
the max amount of work that can be achieved by the system on the surrounding
Wrev = Wmax
what is a irreversible process
cannot be undone by reversing the system
what processes are irreversible
spontaneous process
what phase changes are isothermal process
melting and vaporization
what is the equation for delta S(system) for isothermal processes
nHfus / T
- n = the number of moles
what are the units for entropy
J/K
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
what is the formula for change in universe
change in the system + the change in surroundings
how can you distinguish between the change of system and surroundings
typically by in opposite signs
what is the change in surrounding based on
how much heat is absorbed or given off by the surrondings
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
what does it mean if S(universe) is greater than 0
the reaciton is spontaneous
is the process spontaneous when S(sys), S(surr) and S(univ) is positive
yes
what direction will the reaction proceed if S(univ) is less than 0
it will not proceed in the forward direction
what is the spontaneity of negative system, surrounding, universe
not spontaneous ( occur in the opposite direction)
what will happen if the system is + and the surroundings is -
spontaneous if system is larger than surroundings
what will havppen if system is - and surroundings is +
yes, if the surronding has a larfer magnitude
what is heat also referred to as
enthalpy
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
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
what happens if H <0 and what happens if S <0
the process is exothermic and usually spontaneous
- S <0 then it is nonspontaneous
who developed the relationship between ΔH and ΔS
J. willard gibbs
what is the formula for gibbs energy
G = H – TS
- T is absolute temperature
what is the equation for gibbs when the process is at a constant temp
ΔG = ΔH – TΔS
what is the equation that relates spontaneity to gibbs free enrgy
–TΔSuniv = ΔHsys – TΔSsys
- G = -TΔSuniv at constant T and P
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
what happens when ΔG = 0,
the reaction is at equilibrium
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
why is G preferred of S(univ) to describe spontaneity
g only depends on the system and avoids the complications of the surroundings
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
what happens if H is - and H is + at low temperature and high temp
the reaction is spontaneous
what happens if H and S have different signs
the spontaneity does not depend on the temperature
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
what is heat capacity
the amount of energy needed to raise the temp of a substance
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
what are standard molar entropies
molar entropy values in their standard states
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
- increase with the number of atoms
what is the formula for standard enthalpy change
ΔH° rxn = Σn ΔHf °(products) − Σn ΔHf °(reactants)
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
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
how can you use hf to calculate Gibbs energy
the standard free energies of formation
what is a state function
a property whose value does not depend on the path taken to reach that specific value
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)
how can you make a nonspontaneous reaction spontaneous
coupling it with another process that is highly spontaneous
what do real rxns not achieve
the theoretical limit of available free energy
- irreversible
- −ΔG = ΔG° ONLY under standard conditions
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
as volume increases what happens to the number of potential microstates
the microstates increase, and there is a decrease in pressure
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)
what happens when q < k
excess reactants relative to products meaning the rxn proceeds in the forward direction
when q>k
the rxn proceeds spontaneouslt in the reverse direction
what is the maxium amount of work equal to
change in free energy
what is the work for a nonspontaneous process
G is +, and represents the minimum amount of work
for a spontaneous process what does the work look like
G is (-) and g represents the energy that is free to do useful work
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
what happens when energy is used to do work
it becomes less organized and concetrated so less useful
