330 Exam 2 Flashcards
First Law of Thermodynamics
Energy of the universe is CONSTANT, it interconverts between the system and surroundings (change of energy of the system is equal to the (-) change of the energy in the surroundings)
DeltaG def
The Gibbs free energy tells us if a reaction is sponatneous under a set of condtions
What is a partition function? (q)
THe number of thermally accessible at a given temperature, it is a unitless quantity but it really has stealth units of states
Why must Delta G of a spontaneous process be negative
Bc it increases the entropy of the universe
KT»>E VS. E»>KT
KT> means that that energy levels can be seen as continuous energy spacings at high temperatures
But @ KT<, energy levels are discrete relative to thermal energy and you can get an integral in this case
4 ways to calculate entropy
- S(macrostate) =kln(W)
per mol: **=Rln(W) ** - For a phase transition at constant pressure:** dS=dH/T**
- For heating:
**S= Cpln (T2/T1) ** - Mixing of 2 gasses nk or nR * ln(v1+v2/v2) for each gas and then add them up
2nd law of thermodynamics
For any SPONTANEOUS process dS(of the universe)>0 as the universe is moving toward the most likely macrostate, to get to dS=0
Result of 2nd law of thermodynamics
dSuniverse= dSsys + dS surroundings
so that dSsys + dSsurr >0
dS surroundings = dHsurr/T
(can manipulate this from the first law and say dHsurr=-dHsys
THEN get dHsurroundings=-dHsys/T
2 ways to increase the internal energy of the system
Heat and work
Explain why heat capacity becomes “infinite” at a phase transition (and must approach zero as temperature approaches absolute zero)
Can think about it in terms of statistical mechanics- we are goiong from one collection states to a larger collection of states the temp is not going to heat a substance but to make this transition, hence the temperature does not increase the substance
Rotational partition function energy vs KT
For WIDE energy spacings, hv»>KT so q approaches 1
for small enrergy spacings hv«<KT means that all temps are thermally accessible
Define entropy statistically
How many microstates correspond to a macrostate
Law of large numbers
When we are dealing with very large number of molecules, certain macrostates are so overwhelimingly likely that they are the only thing that we observe
Define a state function
what it means to be either “path-independent” or “path-dependent?”
A state function is a function that obnly dependents on the starting and ending state of a system and NOT the path that it takes to get there
Energy is a state function
BUT the change in energy is not
Work is path dependent
The action of force over a distance, depends on how long the path is
example if you but a boot on a car, the change in energy is the same but if the boot means the car loses energy to friction and you need to increase work and push harder
