Foretelling the Phases of Compound Using Reactants

Yes, there is! All you have to do is look at the phase diagram for the product materials and put the temperature and pressure into it.

Yes, individuals who possess a great deal of knowledge in a specific area of chemistry can usually, but not always, predict the phase (of the three) of the result of a chemical reaction. They usually have extensive knowledge in the section of chemistry that the reaction is part of from either education or experience.

The product of the reaction that you have cited does not usually form a liquid. Placing gaseous H₂ and O₂ in a container, does not react the components. A catalyst, in this case a flame, must be used to cause them to combine. The heat generated by the reaction usually causes the product to be the vapor phase. That vapor phase material, H₂O, must then be cooled to become the liquid phase.

Good Luck, Old Salt

yes during the reaction, depending if its exothermic or endothermic reaction, there can be by-products such as heat or heat has to be applied.

the bonding or the breaking of the chemical bonding just does not happen by itself.

The formation of liquid water from the reaction of hydrogen and oxygen is one of the great surprises in chemistry. Oxygen is in Group 6 of the periodic table - all of which are non-metals - oxygen, sulphur, selenium, tellurium, polonium. Apart from oxygen they all forms gaseous hydrides - H2S, H2Se, H2Te (ignoring H2Po which is an unstable, volatile liquid and radioactive). These are all foul-smelling and poisonous compounds, yet water is completely different. Not only is it a liquid with quite a high boiling point, but also a high latent heat of vaporization, surface tension and of course, essential for life. So why the big difference? All attributed to "hydrogen bonding" - oxygen is highly electronegative and strongly attracts the shared electrons that constitute the bonds with hydrogen, leaving the hydrogen atoms with a fractional positive charge and the oxygen with a negative charge. The attraction of these charges between molecules causes water to be a liquid. Would this have been predicted by a water-less civilization? Almost certainly not.

The same effect occurs to a lesser degree in HF, which is a liquid (only just) whereas HCl and HBr (Group 7 hydrides) are gases.

As to predicting whether a product will be a liquid or solid, much depends on the shape of the molecule and any interactions between them. There are some salts (ionic compounds) that defy all the usual expectations of being crystalline solids and turn out to be liquids - the reason being that either one of the ions present is far bigger than the other or strangely-shaped, and is incapable of undergoing "close-packing" to form a crystal.

These are some of the details that old salt was referring to when he said that some chemists will be able to predict the phase states of a compound molecule from the elements that make it up. The hydrogen bond is one of the big surprises in chemistry that was first considered about a century ago. What fascinates me about hydrogen bonding is that this truly ubiquitous phenomena relies on the shape of the molecules. This is why geometric isomers of unsaturated fats can be liquid or solid at room temperature. Hydrogen bonding is what makes proteins fold and unfold around themselves. Hydrogen bonding is the simple root of some very complicated chemistry.

This is straying but when you brought up unsaturated fats which touches off polymer and monomers.

Company were I work (food ingredients) we deal with this quite a bit in our process.

Such as

• Thixotropic non newtonian fluids

adding energy (Shear force) makes a solid thinner or liquidfy, less viscous.

(Silly Putty, catsup)

and

• Dilantant Non-Newtonian fluids

adding energy that makes a liquid thicker or more rigid, more viscous.

(Mixture of Corn starch and Water mixture) .

Of which is unbelievable interesting.

Thixotropic solutions are great aids in paints. The shear applied by a paint brush allows the material to spread out easily (the viscosity is lowered), but the film does not sag on standing due to the viscosity being rapidly restored.

We developed an additive at I.C.I. Paints Division that would cause hydrocarbons to increase in viscosity (i.e. dilatant) on being subjected to shear - the aim being to prevent jet fuel from spreading widely in an aircraft crash. The trial on a Boeing 720 didn't go too well and the plane was well and truly demolished:

http://en.wikipedia.org/wiki/Controlled_Impact_Demonstration

Paints and some inks.

I recall that trial on the Boeing. Didn't know the reason of how it would help in the spreading of the flames....... now I do, again, quite interesting.

thanks

Most "controlled flights into terrain" don't go too well.

I remember that test, too. In this case the test of flying a full size jet into the ground worked very well. If I remember correctly it proved the theory did work but not well enough to prevent eventual ignition briefly after impact. The test was a success, the concept was flawed.

A great example of hydrogen bonding- even better IMHO than water or HF- is ammonium bifluoride. It is a crystalline substance, a salt of NH⁴:F with a hydrogen bond to an adjacent HF that is almost as strong as the H-F ionic bond. Incidentally, it has a seriously negative heat of solution.

Yes a very good example - thanks!

An alchemist can do this, assisted maybe with a Ouija board.

Mainly if the chemist is named Nostradamus, then the fifth Quatrain of the seventh book, of the fourth volume will provide an obliviated reference to the two elements in question that will present as earth, air, fire, or water. Unless the 16th part of the obscure tome tells of an event in Paris that takes place when Hister arrives on the scene in act one, but then mon amis, you have the fire and the ice.

No. While a chemist will also have to know a lot more than just the elements that make up a molecule to ascertain the phase states of a pure compound, it is not an unknowable attribute to predict.

Yes, but mon ami, there are many exceptions to the rules! Besides that, who would even want to bother "predicting", when there voluminous compendia of available scholarly research on nearly any combination one would want to come up with. The sheer weight of the tomes required serious engineering of libraries to withstand the gravity of the situation (in jest in part).

I for one, as a Ph.D. would not spend more than 30 seconds of a "wet-index finger" guess on such a compound. I would do my library research and get the answer. Besides that, sophomoric chemists have a notorious reputation for "knowing everything there is to know" when the real professional and scholarly chemists know more and more about less and less. The entire field of chemistry is so immense that no one person may comprehend all of it. One example: chemists used to think that all of the silane analogues to the hydrocarbons would be as pyrophoric as simple silane, but later proved to be entirely wrong when Dr.; Plichta discovered and synthesized the higher silanes, found that above a certain silicon number (as in carbon number), they are stable (combustible) liquids at room temperature, at least as safe as gasoline or diesel.

The true challenge (which is nothing but joy for some of us) is to continue the learning curve, to boldly find new things about some aspect of chemistry where no chemist has gone before (to semi-quote Star Trek opening lines), and to apply that knowledge to the solution of some engineering problem, some new materials, new ways to make science work for mankind (instead of against). It requires of a man or woman the highest level of professionalism in the undertaking of science, a moral committment to protect others from harm by the misapplication of chemistry, and challenge to leave the field better than the state in which it was found.

Who would want to predict the phase states of a material, you ask. How about an astrophysicist or anybody trying to plausibly grasp the conditions of an exo-planet or even just simply the engineer asked to design what equipment should be used to harpoon a comet over a decade after assembly and launch. You are certainly correct that there are many exceptions to the rules but to deny the rules exist or that they can be understood is a scientific sin.

Please, don't disturb my circles.

If we were about to embark on such a journey, we already would likely have in hand at least some of the facts about this exo-planet, or the comet we wanted to "harpoon". Having been armed with this, and the knowledge of the location's temperature, pressure, we can easily predict the state of a given molecule at that location. Even if this place is super-hot, we can have a pretty good idea based on the chemistry signature of the atmosphere of what is present, then we compare the makeup of that location to the known facts about the molecules, and if the molecules are not known, we still do not have to guess. We make the stuff and see what it does at P,T. Besides, if this hypothetical molecule is a diatomic one, we can detect it from its radio spectrum that also provides other information such as temperature and pressure. The ab initio boys could calculate the physical properties of the molecule based upon its observed dipole moment, etc.