Session Start: Tue Dec 03 19:01:59 2002
Session Ident: #lecture
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[19:02] <.Silver> when you're ready :))
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[19:02] <.Coppernico> okay
[19:02] <.Coppernico> thanks
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[19:02] <.Coppernico> First of all
[19:03] <.Coppernico> Let's recall several aspects of Thermochemistry
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[19:03] <.Coppernico> It's interesting
[19:03] <.Coppernico> to speak of the laws of the thermodynamics
[19:04] <.Coppernico> The first law of thermodynamics state that energy can be converted from one form into another
[19:04] <.Coppernico> but that energy cannot be created nor destroyed
[19:05] <.Coppernico> This idea sounds easy to understand nowadays
[19:05] <.Coppernico> but it has a lot of consequences in the development of science.
[19:06] <.Coppernico> Much of the advanced theories mankind have so far developed uses this law.
[19:06] <.Coppernico> Or is only possible because of it
[19:06] <.Coppernico> Let's define for now what's a system.
[19:07] <.Coppernico> A system is mere a part or a set of something we want to analyse
[19:07] <.Coppernico> therefore we say that this and this are in the system and that and that are not
[19:08] <.Coppernico> A system is therefore a man-defined institution to facilitate the study of a phenomena
[19:08] <.Coppernico> Everything that is outside a system by us defined is called the surroundings.
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[19:09] <.Coppernico> As the first law of thermodynamics, which I might call only first law states
[19:09] <.Coppernico> the internal energy of an isolated system
[19:09] <.Coppernico> is constant
[19:10] <.Coppernico> by isolated system let's understand that it's a system without anykind of interaction with the surroundings
[19:10] <.Coppernico> Also, It's very interesting to know 
[19:11] <.Coppernico> that energy is a state function, what means that a energy of system depends only of the system actual situation, and does not depend on how the system got to this configuration.
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[19:12] <.Coppernico> Therefore we can say that in a process, independent of how this process succeded, that the energy variation equals the energy of the final state minus the energy of the initial state
[19:13] <.Coppernico> There are two ways of having a system into a process:
[19:14] <.Coppernico> One of them is by giving heat to it of geting heat from it
[19:14] <.Coppernico> other way is to compress or expand this system, by means of changing the volume it occupies in the space.
[19:15] <.Coppernico> For instance, we know that in the gases, processes are due to the changes of those variables.
[19:15] <.Coppernico> We might now, get a little further on definitions
[19:17] <.Coppernico> We know that the work, in ordinary chemical reactions, arises as a consequence of changes in the pressure and volume of the system. And a mathematical analysis shows that the work is equal to the internal pressure of the system 
[19:18] <.Coppernico> times the variation of the volume that ocurried in the process.
[19:18] <.Coppernico> Therefore a process with constant volume or isovolumetric is completely absent of work.
[19:19] <.Coppernico> Let suppose an isovolumetric process then.
[19:20] <.Coppernico> We can then say that, in this process at constant volume, the variation of the internal energy is due only to heat exchanges among inside the system and the surroundings.
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[19:21] <.Coppernico> It's a nice simplification, but in chemistry, process conducted at constant pressure are more common than those in constant volume
[19:21] <.Coppernico> and thus this simplification is of more seldom use.
[19:22] <.Coppernico> Please accept that [] stands for Delta , or variation of a quantity, []V means, for instance , the Delta of Volume
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[19:22] <.Coppernico> We have in this pressure constant system that
[19:23] <.Coppernico> Obs. In case of a doubt, ask me on the PVT and I'll post the message in here.
[19:23] <.Coppernico> Getting back, 
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[19:23] <.Coppernico> We have that
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[19:24] <.Coppernico> []E = q - P.[]V
[19:24] <.Coppernico> thus
[19:24] <.Coppernico> q = []E + P.[]V
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[19:25] <.Coppernico> what means that:
[19:25] <.Coppernico> q = (E1 - E0) + P.(V1 - V0)
[19:25] <.Coppernico> let's explain thus that q means heat
[19:26] <.Coppernico> and 1 is the final state
[19:26] <.Coppernico> 0 is the initial state
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[19:26] <.Coppernico> It's of interesting use to define a new function
[19:26] <.Coppernico> called enthalpy(H)
[19:27] <.Coppernico> let's define it as H = E - P.V
[19:27] <.Coppernico> and by this definition 
[19:27] <.Coppernico> and easily get that
[19:27] <.Coppernico> q = H1 - H0
[19:27] <.Coppernico> and thus q = []H
[19:28] <.Coppernico> we have than that
[19:28] <.Coppernico> []H = []E + P.[]V
[19:29] <.Coppernico> Would be nice to suppose now
[19:29] <.Coppernico> a reaction among gases
[19:29] <.Coppernico> exclusively gases.
[19:29] <.Coppernico> You might know the ideal gases equation
[19:29] <.Coppernico> it goes like P.V = n.R.T
[19:30] <.Coppernico> R is a constant, n is the number of moles of gas
[19:30] <.Coppernico> we can write that 
[19:30] <.Coppernico> for a constant pressure P
[19:31] <.Coppernico> P.V0 = (n0). R.T
[19:31] <.Coppernico> and
[19:31] <.Coppernico> P.V1 = (n1). R.T
[19:31] <.Coppernico> Just a recall, T stands for the temperature in which the process is occuring
[19:32] <.Coppernico> make the latter equation minus the former and get:
[19:32] <.Coppernico> P.V1 - P. V0 = (n1).R.T - (n0).R.T
[19:32] <.Coppernico> P(V1 - V0) = RT.(n1 - n0)
[19:33] <.Coppernico> P.[]V = RT.[]n
[19:33] <.Coppernico> and on this exclusive process:
[19:33] <.Coppernico> []H = []E + []n.R.T
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[19:34] <.Coppernico> wow
[19:34] <.Coppernico> enough for now about the first law
[19:34] <.Coppernico> about about getting on the second law of thermodynamics?
[19:35] <.Coppernico> okay
[19:36] <.Coppernico> this law has an imporant hole in predicting whether a process is spontaneous or not.
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[19:36] <.Coppernico> Let define a new funtion
[19:37] <.Coppernico> the entropy(S) which is fundamental to the second law.
[19:37] <.Coppernico> The best interpretaion for it is a measure of the randomness or the disorder level of a system
[19:37] <.Coppernico> thus
[19:37] <.Coppernico> high disorder --> high entropy
[19:39] <.Coppernico> You know disorder is statistically more probable than order, what makes possible the we can regard it as probability function.
[19:39] <.Coppernico> but for now, let's say the second law:
[19:40] <.Coppernico> EVERY SPONTANEOUS CHANGE IS ACCOMPANIED BY AN INCREASE IN ENTROPY
[19:41] <.Coppernico> This variation on the entropy is given by:
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[19:41] <.Coppernico> total []S = system[]S + surroundings[]S
[19:43] <.Coppernico> acutually, surroundings[]S  is equal to minus the division of the []H of th process per the temperature in which it occurs
[19:43] <.Coppernico> surroundings[]S = -[]H/T
[19:44] <.Coppernico> we have than
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[19:45] <.Coppernico> total[]S.T = []S.T - []H
[19:46] <.Coppernico> thus
[19:46] <.Coppernico> -total[]S.T = - []S.T + []H
[19:47] <.Coppernico> -total[]S.T = []H - []S.T
[19:47] <.Coppernico> let's then finally get to define the topic of the lecture
[19:47] <.Coppernico> the gibbs free energy(G)
[19:47] <.Coppernico> is defined as : G = H - TS
[19:48] <.Coppernico> so that []G = []H - T.[]S
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[19:49] <.Coppernico> if total[]S is greater than zero for a spontaneous change, T.total[]S ,must be greater than zero, -T.total[]S must be less than zero.
[19:50] <.Coppernico> In a spontaneous change, []G < 0
[19:50] <.Coppernico> for a system in chemical equilibrium, []G = 0
[19:51] <.Coppernico> and in a forced change, []G > 0
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[19:51] <.Coppernico> This function
[19:51] <.Coppernico> have a very interesting analysis
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[19:52] <.Coppernico> which is the real union of two of the most certain tendencies.
[19:52] <.Coppernico> 1 - Get to the smallest level of potential energy
[19:52] <.Coppernico> 2 - Get the universe to a more disordered one.
[19:53] <.Coppernico> we see that the spontanity of a process depends on these tendencies
[19:53] <.Coppernico> for that the []H measures, somehow, the tendency one
[19:54] <.Coppernico> and total[]S measures the tendency 2
[19:54] <.Coppernico> thus, this wonderful function
[19:54] <.Coppernico> in this simple mathematical equation 
[19:54] <.Coppernico> is the responsible for giving man power to predict whether something can or cannot occur
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[19:55] <.Coppernico> make good use of the prediction powers, because that can make you a much more valuable man.
[19:55] <.Coppernico> thank you all
[19:55] <.Coppernico> hope you liked.
[19:55] * Coppernico sets mode: -m
[19:55] <.amb> Yes! :-)
[19:55] * Coppernico sets mode: -o Coppernico
[19:55] <.amb> It was nice!
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[19:56] <.Silver> thanx Coppernico :))
[19:56] <.Silver> !lect off
Session Close: Tue Dec 03 19:56:08 2002