rh@mit-eddie.MIT.EDU (Randy Haskins) (12/27/86)
I've forgotten my organic chem, and I don't know anyone around me who remembers theirs. I remember there being some relationship between Entropy (S), Enthalpy (H), and Gibbs' Free Heat (G). Can someone out there send me a brief description of the relation and what each of these quantities mean physically? adTHANXvance Random genrad!mit-eddie!rh -- Randwulf (Randy Haskins); Path= genrad!mit-eddie!rh
apn@nonvon.UUCP (apn) (12/29/86)
In article <4383@mit-eddie.MIT.EDU>, rh@mit-eddie.MIT.EDU (Randy Haskins) writes: > I've forgotten my organic chem, and I don't know anyone around me > who remembers theirs. I remember there being some relationship > between Entropy (S), Enthalpy (H), and Gibbs' Free Heat (G). > Can someone out there send me a brief description of the > relation and what each of these quantities mean physically? > adTHANXvance > > Random > genrad!mit-eddie!rh > -- > Randwulf (Randy Haskins); Path= genrad!mit-eddie!rh Hope this serves to reduce the entropy rather than increase it. ENTHALPY .... A measure of Energy (usually heat) given off or absorbed in a given reaction. delta H := delta E + P * delta V P = presure, E energy, H Enthalpy this eq. is true for constant presure. i.e. delta H would be negative for an exothermic reaction note that this is a state function and therefore one only needs to know the starting and ending conditions to calc. the delta H. ENTROPY .... Either form of the second law of Thermodynamics leads us to a new function .... delta S delta S = q/T If an amount of heat , q, is added to a system with a temperature of T, then entropy increases by amount delta S. Now, according to boltzmann , entropy is also a measure of disorder on a system ( and hence the keywords of this article followup ) Boltzmann proposed that entropy, S, is related to the number of different microscopic ways ways of obtaining a specified macroscopically definable and observable situation. hence we obtain, S = k ln W where W, is the number of equivalent ways to contruct a given situation, S is ( obviously by now ! ) the entropy. and it naturally follows since this relationship was discovered by boltzman , that k *is* the boltzman constant. numerically, and dimensionally however, it is equates as follows: k = R/N N = avogadro's number, R is the "ideal" gas constant expressed in your favorite units. ( side note: this also gives us the dimensions in S since the ln function yields a non - dimensional value ) when we combine the relationship that was given to us by boltzman and the one from the first law of Thermodynamics (claisus, I believe ). we get one of the most radical and important theories of present science. Or more simply put, In any real, spontaneous processes, including, but not limited to, chemical reactions, the disorder of the universe always increases. This, for example is useful for explaining the general state of my home, or my office desk. Now... back towards your original question.... In any isolated system, in which the total E cannot change, a spontaneous reaction is one in which entropy ( and by definition , disorder ) increases. No process that produces order, or lowers the entropy, can occur WITHOUT outside help. (analogious to rearranging my desk to some order ) Outside help is naturally in to form of some energy.. And then there is Delta G, or a measure of free energy. Any given chemical equilibrium system not only seeks the lowest energy at enthalpy, but also the greatest state of disorder, probability , or entropy, S. Therefore a new state function has been defined: free energy := G := H - TS Reactions at constant T, and P are spontaneous iff ( note iff not if ) the free energy, G, increases. In a given equilibria in a closed system at constant T, and P, we have: delta G = delta H - T * delta S So, to summarize [ read: explanation of above equation ]: In any spontaneous rxn, at constant T and P, the free energy G, always decreases. When the rxn system reaches equilibrium, G is at a MINIMUM, and dG is zero (Did I just say the same thing twice ? ) For a *real* definative study of entropy, time, and complexity, I very highly recommend the book _From Being to Becoming_ by Ilya Prigognine Freeman/ Univ. of Brussels. ( no, this book has no relation to The Forum ) But I warn you, be prepared for hamiltonian, matter wave equations, potential wells, manifolds, and in general lots of linear algebra. -alex p novickis UUCP: ihnp4!ptsfa!nonvon!apn 100 Drakes Landing Road GreenBrae, CA 94904 {* Only those who attempt the absurd ... will achieve the impossible *} {* I think... I think it's in my basement... Let me go upstairs and check. *} {* -escher *} -- UUCP: ihnp4!ptsfa!nonvon!apn 100 Drakes Landing Road GreenBrae, CA 94904 +1 415 461 4655 {* War does not determine who is right or wrong........ only who is left *} {* Only those who attempt the absurd ... will achieve the impossible *} {* I think... I think it's in my basement... Let me go upstairs and check. *} {* -escher *} {* System down for P.M. until further notice *}