[ayslam]

Dear All,

I would like to ask some questions about chemical reactions, and to say sorry if it is not the right place to ask my questions. According to my knowledge, chemical reaction is a process to bring the reactants into products. It may undergo several elementary steps before finally reach the product stage. If we consider the situation in terms of  potential surface, the chemical components start from the form of reactants and go uphill and downhill several times before changing into the products. Under different circumstances, the products may be different. I would like to ask:

1. Are there any rules or laws governing the chemical process?
2. How can the products be determined? Why is the final product "chemical A", but not "chemical B"?
3. Why do chemical reactions carry on? Is it because the products are more "energy stable" than the reactants?
4. Are there any computer softwares which can simulate chemical reactions? says if I provide the reactants and their amounts, and set up the temperature and pressure and etc. can the software determine the products for me?

I am not studying chemistry and these are not my homework. Instead, I am an engineering student and the nature of chemical reaction processes relates to my works. I would appreciate if someone could ask me those questions.
Thank you for your attention.
Best Regards,
Albert

[Yggdrasil]

1. Are there any rules or laws governing the chemical process?

There are a some.  Some laws relate to the thermodynamics of the reaction (i.e. under what conditions is the reaction favorable?  when does the reaction go forward and when does it go backward?  how much energy does the reaction require/release?) and other relate to the kinetics (i.e. how fast does the reaction proceed?).

2. How can the products be determined? Why is the final product "chemical A", but not "chemical B"?

Although there are some general rules of thumb, they are all derived empirically.  So, if the reaction is similar to a reaction that someone has done before, you can guess at what the products will be, but the ultimate answer is always to mix the chemicals and see what comes out in the end.  In theory, you may be able to look at how the molecular orbitals of the two reactants interact, but I'm not aware of any programs that can do this.

3. Why do chemical reactions carry on? Is it because the products are more "energy stable" than the reactants?

Yes.

4. Are there any computer softwares which can simulate chemical reactions? says if I provide the reactants and their amounts, and set up the temperature and pressure and etc. can the software determine the products for me?

Not that I know of.  There are some databases, where if you put in reactants and products, the computer will search through a database of reactions then spit out a set of reactions and their conditions, but I do not know of any programs which can predict reactivity ab initio.

(note: I have not studied this topic at an advanced level, so there may be some programs that I do not know about which can predict simple reactions ab initio, but I doubt that there are any programs which can simulate more complex reactions).

[enahs]

Your question pretty much why people study chemistry. Those question are some of the most basic fundamental question that allowed us to establish what we know and continue to allow is to learn.

If somebody could summarize nearly the whole field in chemistry in a forum post, then wow!

[ayslam]

Thank you for your favorable responses. But I would like to know more about these, I do not have enough time to study whole field of chemistry.

1. Are there any rules or laws governing the chemical process?
If there are some rules, then what are they? As there may be many elementary steps in a reaction process, how can the reactants go through the 1st elementary step and reach the intermediate state? and the 2nd, 3rd.... Do they collide to each other and exchange some energies? Those have collected enough energy (to overcome the activation energy) go through the steps in this way?

2. How can the products be determined? Why is the final product "chemical A", but not "chemical B"?
If there are some rules of thumb, then what are they?

4. Are there any computer softwares which can simulate chemical reactions? says if I provide the reactants and their amounts, and set up the temperature and pressure and etc. can the software determine the products for me?
What are the computer software which can handle these tasks?

I would like to know more about these topics. Could you please tell me which specific areas of chemistry I should stick into?
Thank you for your great help.

[Ψ×Ψ]

3. Why do chemical reactions carry on? Is it because the products are more "energy stable" than the reactants?

Whoa!  If this were the case, all reactions would be exothermic.  Not true!  You're leaving out all the kinetics!  Also, some reactions are driven by entropy.

[Yggdrasil]

1. Are there any rules or laws governing the chemical process?
If there are some rules, then what are they? As there may be many elementary steps in a reaction process, how can the reactants go through the 1st elementary step and reach the intermediate state? and the 2nd, 3rd.... Do they collide to each other and exchange some energies? Those have collected enough energy (to overcome the activation energy) go through the steps in this way?

This question is way too complicated to answer through a forum.  I would suggest and advanced courses in thermodynamics and kinetics to start.

2. How can the products be determined? Why is the final product "chemical A", but not "chemical B"?
If there are some rules of thumb, then what are they?

Again, too many to enumerate through a forum post.  Most of them you would pick up though an advanced study of organic chemistry or the field whose chemistry you're trying to become familiar with.

Whoa!  If this were the case, all reactions would be exothermic.  Not true!  You're leaving out all the kinetics!  Also, some reactions are driven by entropy.

I was thinking in terms of free energy rather than enthalpy.  But you are right that in order for a reaction to occur, it must be kinetically favorable as well as thermodynamically favorable.

[Donaldson Tan]

1. Are there any rules or laws governing the chemical process?
If there are some rules, then what are they? As there may be many elementary steps in a reaction process, how can the reactants go through the 1st elementary step and reach the intermediate state? and the 2nd, 3rd.... Do they collide to each other and exchange some energies? Those have collected enough energy (to overcome the activation energy) go through the steps in this way?

From thermodynamics, it is possible to identify all the potential chemical reactions that may take place. In fact, this method (ie. plotting free energy G of reactants and that of potential products vs Temperature T at a fixed pressure) is employed in the analysis of industrial chemistry to identify all the side reactions that might take place in a reactor given the operating conditions. However, it is the kinetics that will decide what the major product is since different operating conditions favour different reaction kinetics at varying degree. A chemist would call this kinetics control but from a chemical engineering point of view, I would call this reaction engineering. By designing the reactor, controlling the flow rate, extent of mixing and positioning of catalysts and point of heat input, chemical engineers can control the quality and the selectivity for a desired chemical product.

One of the simplest chemical reactor that would best demonstrate what I had said is the Iron Blast Furnace. Iron Ore consists of mainly Fe₂O₃ and some impurities such as sand (SiO₂) and CaCO₃. The design of the Iron Blast Furnace is quite elegant because it allows in-situ separation of product (molten iron) and the unwanted components (slag) in virtue of their difference in density. Product separation and purification are often the most pressing and complicated issues in designing a modern chemical plant (eg. PUREX process for processing spent nuclear fuel).

However, what makes the Iron Blast Furnace reaction really interesting is that the reducing agent of Iron (III) Oxide is not Coke but Carbon Monoxide. Most people would think that Coke is the reducing agent of Iron(III) Oxide since it is one of the feedstock. However, at the operating temperature beyond 1500C, CO is a far stronger reducing agent than Coke and it is formed in-situ in the furnace by the reduction of CO₂ (from thermal decomposition of CaCO₃) with Coke. You would arrive at this conclusion if you had plotted the graph I mentioned earlier.

If you are interested in controlling industrial chemical reactions, I would recommend you to read these courses:
1. Chemical Engineering Thermodynamics
2. Kinetics of Chemical Reactions
3. Chemical Reaction Engineering

[tamim83]

True, thermodynamics tell us if a reaction is "favored".  For example we learn that negative delta G means that a reaction will be spontenious and so one but even some of these reactions do not happen.  This is were kinetics come in.  In kinetics, we look at energy too, but in a different way.  Every reaction has an energy barrier to overcome, If it doesn't traverse this barrier, it's a no go, no matter how spontenius the reaction will be.