Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Neverquit on January 26, 2011, 01:36:17 PM
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Hi,
I have seen all sorts of answers to this from gibbs energy to equilibrium constant to analogies.
I'm pretty sure its got to do with the energy, enthalpy and collision theory but I can't get a clear cut definition of it. Can anyone help?
Regards,
Neverquit
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What do you understand to be the relationship between the equilibrium constant of a reaction and its ease or difficulty to reverse?
Under what conditions is the equilibrium constant of a reaction not a constant?
Can you articulate what it is about Gibbs Free Energy that you understand and where you get stuck?
What do you understand about the overall entropy change of a system compared to the entropy of the environment that affects the position of equilibrium of a chemical reaction?
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What do you understand to be the relationship between the equilibrium constant of a reaction and its ease or difficulty to reverse?
Something to do with temperature and proportionality of concentrations of ions? If you change the concentration of one it must change the concentration of another to be constant?
Under what conditions is the equilibrium constant of a reaction not a constant?
Something to do with temperature?
When equilibrium is not reached?
Can you articulate what it is about Gibbs Free Energy that you understand and where you get stuck?
I’m not fully versed in Gibbs.
What do you understand about the overall entropy change of a system compared to the entropy of the environment that affects the position of equilibrium of a chemical reaction?
Entropy relates to the flow of energy. Eg. Heat will flow in the direction towards the colder area. Or the direction of a reaction ie forward or reverse?
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Hi,
nobody can help me?
Regards,
Neverquit
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let's reason differently:
let's assume a reaction at equilibrium.
A+B <--> C
is it hard to reverse this? In other words, is it hard to make the reaction go backwards?
Well, the position of the equilibrium depends (amongst other things) on the amount of reactants available (for example, if C is a gas that evolves, the reaction will be indeed hard to reverse as one of the reactants, C, effectively gets removed from the solution/reactor)
But what if we forcibly supply more and more C, then the reaction will go backwards!
Read up on Le Chatelier's principle for equilibrium changes.
And yes, the equilibrium constant is related to the change in gibbs free energy (dG = -RT ln Keq), which is itself dependent on changes in enthalpy and entropy.
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To put it simply...
Thermodynamics. If the products are very stable there is no motivation to them to reform reactants. Look at explosives for instance, they produce CO2 N2, H2O etc... when was the last time you saw anyone take these three things, mix them together and get TNT to come out?
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why are reactions taking place?
Universe favors more stable products.During a reaction a more stable product is formed and hence reversal in the direction of less stability is not favored by the universe.
Everything happening in this universe is the flow in the direction of less energy and more stability .If the products have more energy than the reactants then reversal of the reaction is favored .
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It's harder to walk up a hill than down it.
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again because you are more stable at the bottom of the hill with minimum potential energy
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why are reactions taking place?
Universe favors more stable products.During a reaction a more stable product is formed and hence reversal in the direction of less stability is not favored by the universe.
Everything happening in this universe is the flow in the direction of less energy and more stability .If the products have more energy than the reactants then reversal of the reaction is favored .
Not true, although admirable. This "less energy" theory is simply wrong.
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It's kind of right.
A chemical reaction proceeds in the way which lowers the energy stored in the molecules electric fields. There's some necessary fine tuning but it's pretty much right as far as I know.
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It's true that everything proceeds towards stability, but to say that systems naturally go towards states of lower energy is not true. This would contradict the first law of thermodynamics.
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its actually because of a combination of all the above discussed factors ;)
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All irreversible (spontaneous) reactions happen because of entropy.
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I can offer a reaction kinetics view I guess. Let's take 408's TNT example. Now it is possible that there is some wacky reaction mechanism that allows for H2O, CO2, and N2 to form TNT. So why don't we see it happening? The reason is there is probably a very high activation energy to convert those three compounds into TNT. We can easily get TNT to make water, carbon dioxide, and nitrogen by lighting a fuse.
Thermodynamics (free energies and equilibrium constants) can tell us how stable products or reactants are and perhaps which are more "favorable". Kinetics can tell you how easy it is to make the transformation (how big of a hill do you need to climb).
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We can easily get TNT to make water, carbon dioxide, and nitrogen by lighting a fuse.
If by fuse you mean fuse with a detonator, then yes :P
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If by fuse you mean fuse with a detonator, then yes
Yep ;D
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TNT is a rather complex molecule. Why not use a simple example like N2 + 3H2 <=> 2NH3
or H2 + Cl2 <=> 2HCl
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All irreversible (spontaneous) reactions happen because of entropy.
its not necessary that an irreversible reaction will be spontaneous always... ;)
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All irreversible (spontaneous) reactions happen because of entropy.
its not necessary that an irreversible reaction will be spontaneous always... ;)
Such as?
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nstance, the decomposition of carbonic acid (H2CO3) into water and carbon dioxide (H2O and CO2) is spontaneous. However, it can be reversed by an enzyme called carbonic anhydrase; it just takes energy.
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Enzymes don't change the energetics of the reaction. They only affect the kinetics. Carbonic anhydrase doesn't "reverse" the reaction; the reaction itself is always reversible. The position of the equilibrium is unaffected. The role of carbonic anhydrase is to bring the reaction to an equilibrium rapidly.
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He didn't word it this way but I think he means the entropy of a closed system can decrease if heat is added.
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He didn't word it this way but I think he means the entropy of a closed system can decrease if heat is added.
The entropy of a closed system would increase if heat is added, actually. Regardless, the entropy of the universe cannot decrease. When :delta: S is negative for a reaction, only the entropy of the system decreases; that of the universe cannot.
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He didn't word it this way but I think he means the entropy of a closed system can decrease if heat is added.
The entropy of a closed system would increase if heat is added, actually. Regardless, the entropy of the universe cannot decrease. When :delta: S is negative for a reaction, only the entropy of the system decreases; that of the universe cannot.
That's why I said system and not universe. And I take by the heat part and change to some reactions. There are endothermic combination reactions where heat increases the number of products but reduces the entropy. Granted, can't think of any off the top of my head.
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An endothermic reaction in which entropy decreases would not be spontaneous.
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An endothermic reaction in which entropy decreases would not be spontaneous.
Ya know, I've read of endothermic synthesis reactions but I was walking to Ralphs thinking, that doesn't make any sense though...I have to agree with you, I either read something wrong or I need to reread it.