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Liamatpm
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[*] posted on 9-12-2016 at 09:06
How to predict/calculate chemical reactions


How can you predict/calculate chemical reactions?

I am talking about acid+base=water +salt, base+water, acid+water, salt+ water, acid+ salt and base+salt. Thank you!

(Any help would be very appreciated!)

-Liam
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Sulaiman
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[*] posted on 9-12-2016 at 09:18


Quote: Originally posted by Liamatpm  
How can you predict/calculate chemical reactions?

I am talking about acid+base=water +salt, base+water, acid+water, salt+ water, acid+ salt and base+salt. Thank you!
-Liam


initially and until now, I have found that the best way is to google it :D
just type in the 'ingredients' and click to have more information than time. (I avoid yahoo answers and like Wikipedia)
there are so many rules and exceptions to remember,
and it has all (mostly) been done before and documented.




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[*] posted on 9-12-2016 at 09:21


Any reasonable textbook will explain the basic types of chemical reactions, and then you build on those.



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Liamatpm
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[*] posted on 9-12-2016 at 09:29


Thank you will try go get a chemistry textbook. Thanks again!
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Sulaiman
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[*] posted on 9-12-2016 at 11:30


SM has a library http://library.sciencemadness.org/library/index.html
I liked
The Golden Book of Chemistry Experiments
Handbook of Preparative Inorganic Chemistry
Simple Chemical Experiments
later you can read more specific and technical documents

also web sites like
http://woelen.homescience.net/science/chem/index.html

I recommend looking at YouTube chemistry videos,
chooing a couple that interest you,
do what you can to prepare to reproduce the experiment,
then do the experiment yourself - if it looks safe to do so,
if not, or any doubts, ask a question here on SM
. give a reference to the experiment that you wish to perform
. explain your question
and you will almost always get help.




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[*] posted on 9-12-2016 at 12:00


Quote: Originally posted by Sulaiman  
SM has a library http://library.sciencemadness.org/library/index.html
I liked
The Golden Book of Chemistry Experiments
Handbook of Preparative Inorganic Chemistry
Simple Chemical Experiments


These don't explain the concepts of chemical reactions, though, which is what the OP is looking for.

This one is somewhat childishly written, but gives what you're looking for:
https://opentextbc.ca/introductorychemistry/chapter/the-chem...




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[*] posted on 10-12-2016 at 18:11


I have always wondered this, (and I wanted to post about it) I read the link you provided but it looks really simple (things like 2H2 + O2 + 2H2O)

I want to know why (as an example, taken from doctor klawonn thread because is the one I was looking at right now)

2 MnO(OH) + NaHSO3 + 3 NaHSO4 --> 2 MnSO4 + 2 Na2SO4 + 3 H2O

so why this happens?, and we don't produce manganese sulphide, or sulphur dioxide, or NaOH (those are a bit dumb but I'm just exaggerating)

I know its related to electronegativity and reactivity and such, my question is if having the adequate charts (with the elements in order of electronegativity and more information) we can predict the reaction (complicated ones maybe involving 3 or 4 different chemicals)
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[*] posted on 11-12-2016 at 01:49


to determine if that formula is valid WITHOUT references you would have to determine the energy change and activation energies required for all possible results
including manganese sulphide, or sulphur dioxide, or NaOH ... and others that you may not have thought of.

The most likely products will be the ones that overall cause the most heat loss, or lowest energy level,
but there will almost always be some of the unexpected species around from other possible combinations because temperature is atomic movement - random jiggling about - bending, breaking and re-making bonds bazillions of times per second at room temperature - chaos!

but why do endothermic processes proceed ? - I have no idea :P

[Edited on 11-12-2016 by Sulaiman]




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[*] posted on 11-12-2016 at 04:31


Quote: Originally posted by Sulaiman  

but why do endothermic processes proceed ? - I have no idea :P

[Edited on 11-12-2016 by Sulaiman]


Sufficient increase in entropy of the system.

ΔG = ΔH - TΔS




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[*] posted on 11-12-2016 at 06:20


could you elucidate a little ?



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[*] posted on 11-12-2016 at 13:33


A reaction will proceed if it results in an overall increase in the entropy of the universe. Most exothermic reactions are spontaneous because the heat they give off will increase the entropy of the surroundings. Reactions that are endothermic can proceed if they result in a large increase in internal entropy. Ice melting, for example, takes heat out of the surroundings (reducing their entropy), but increases its own entropy enough to compensate for this (because liquids are more entropic than ordered crystals).

To predict a reaction such as the manganese one, read up about redox reactions. Mn(III) is a strong oxidizing agent, and sulphite is a pretty good reducing agent. To turn sulphite into sulphide, you would have to *reduce* it, and that's not going to happen in the presence of Mn(III).




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[*] posted on 11-12-2016 at 21:15


the manganese reaction was an example, so as for redox this is fairly "simple" you need your oxidizer and your reducing agents and so on, but I was talking about a way of predicting which reaction is going to increase the entropy on the highest level possible for that reaction.

So taking a simple redox: CuSO4 + 2NaOH -> Cu(OH)2 + Na2SO4

this doesn't happen because you have an oxidizer and a reducing agent (well it does but...) ultimately this happens because this is the reaction that increases the level of entropy the most (of the possible reactions within those components obviously)

So that was my real query if we can get the final answer of a reaction from a "universal test" (that can predict the outcome of any reaction because it predicts the highest increase of entropy possible, being it redox, acid base, substitution etc)

Edit: what sulaiman wrote seemed interesting because it gives a way of "predicting" this : " you would have to determine the energy change and activation energies required for all possible results" that probably is easier said than done (and of course you would have to come up with a real formula because we won't be able to calculate this for every single compound that could or couldn't be produced)

[Edited on 12-12-2016 by exodia]
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[*] posted on 12-12-2016 at 16:09


Quote: Originally posted by Sulaiman  
could you elucidate a little ?


To elucidate a little on that:
"Sufficient increase in entropy of the system.

ΔG = ΔH - TΔS
"

This is the equation for calculating the Gibbs free energy (ΔG).

A reaction will only proceed (at a constant pressure-volume product) without the addition of energy if ΔG is negative, meaning that energy is lost by the chemical system and released to the surroundings. Such reactions are said to be exergonic.

For an unfavorable reaction ΔG is has a positive value, meaning that energy is absorbed by the chemical system from the surroundings. Such reactions are said to be endergonic.

What are those ΔH and TΔS terms?

ΔH is the change in energy to the system (called enthalpy), and can be calculated from the heats of formation of the reactants and products. This part is pretty much intuitive.

TΔS is the temperature-dependent entropy term. This measures the amount of randomness in the system. A reaction that results in more products than reactants increases entropy, giving ΔS a positive value, and favoring the reaction. A reaction that produces fewer productions (a condensation or addition perhaps) reduces entropy and is negative. This is not intuitive and probably rather surprising.

It is also important to understand equilibrium constants K.

Other important factors to understand are relative strengths of acids (and their conjugate bases) and degrees of electronegativity.

[Edited on 13-12-2016 by careysub]




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