
Questions about the final and/or course?
A blog for the physical chemistry course sequence at Cal Poly, particularly CHEM 351, 352, and 353.
∆Suniv ≥ 0 [= for equil/reversible, > for spont/irreversible]Unfortunately, abuses of this statement are many and takes but a moment's googling to find them. For many scientists, it holds a special place:
The law that entropy always increases-the second law of thermodynamics-holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations-then so much the worse for Maxwell's equations. If it is found to be contradicted by observation-well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation." – Sir Arthur Eddington [1928]And to reiterate some general statements from class, which will hopefully help you more fully grasp spontaneity and reversibility:
All spontaneous processes are irreversible.Some common misstatements about the Second Law:
For all irreversible processes, ∆Suniv > 0.
All reversible processes are at equilibrium.
For all reversible processes, ∆Suniv = 0.
All systems tend to greater disorder.Before moving onto specific applications of the Clausius relation, we paused, for bookkeeping's sake, to mention the Zeroth Law: If systems A and B are in equilibrium, and systems B and C are in equilibrium, then systems A and C are in equilibrium. Not only does this establish that a state property common to them must be equal (the temperature), it also allows for the possibility that two systems could be in equilibrium without in direct contact.
False: Not only is "disorder" a poorly constructed idea and overly dependent on human interpretation, the underlying premise is wrong.
All systems tend towards greater entropy.
False: Some systems tend towards greater entropy while others don't. The restriction rests on ∆Suniv, not on ∆S.
First Law - limits the magnitude of energy transferBefore discussing how it was first discovered, we first needed to correct some misconceptions about entropy, one of the most thoroughly mangled concepts in all of science:
Second Law - limits the direction of energy transfer
Entropy is not equal to disorder, nor is it a measure of disorder (whatever that means scientifically).One of the most common [bad] examples demonstrating the alleged relationship between entropy and disorder is a deck of cards. When we shuffle an "ordered" deck of cards, we always see it become "disordered". The problem with this language is that there is no way to quantify order, especially since every outcome is equally probable. We have simply defined A,2,3,4 .. Q,K of each suit as being the ordered state -- but that definition is arbitrary. Nature should not -- and does not -- depend on such human definitions. Other [bad] examples include blaming messy desks and cluttered rooms on this "law of entropy."
When we connect it directly to the number of accessible microstates (ala Boltzmann) we will understand the probabilistic basis of entropy more fully.
Entropy is a measure of the tendency of energy to disperse, rather than being localized.
CP,m = 20.9 + 0.042T ( T in K, CP,m in J K-1 mol-1)It is important for you to understand why this gas is necessarily nonideal, despite the fact that the question states otherwise. In fact, for reasons stated above, it is not even possible to calculate a value for ∆U, which is also important for you to understand.
The study of physics has driven us to the positivist conception of physics. We can never understand what events are, but must limit ourselves to describing the pattern of events in mathematical terms: no other aim is possible .... the final harvest will always be a sheaf of mathematical formulae. (Sir James Jeans)
How can it be that mathematics, a product of human thought independent of experience, is so admirably adapted to the objects of reality? (Albert Einstein)
Mathematics has the completely false reputation of yielding infallible conclusions. Its infallibility is nothing but identity. Two times two is not four, but it is just two times two, and that is what we call four for short. But four is nothing new at all. And thus it goes on and on in its conclusions, except that in the higher formulas the identity fades out of sight. (Johann Wolfgang Von Goethe)
Lecture Five found us [re]examining the concept of energy, momentarily reflecting on the fact that it is, at heart, a defined rather than measured quantity. So the principle of the Conservation of Energy is, simply, the statement that humanity has stumbled onto some number that happens to never change for the universe. This is a direct consequence that the laws of physics do not appear to change with time.