A question to all you learned chemists

[Guest sedition]

You might consider this question to have an obvious answer but, sadly, I don’t! So, let me begin to explain my predicament.

When, say, 1M of Na is reacted with 1M of HCl the equation will be as follows:

Na + HCL ---> NaCl + ½ H2

 

This reaction is supposed to be vigorous because so much H gas is released. However, according to my calculations, only 1g of H2 will be released from the above equation if both Na and HCl are themselves of 1M quantity.

In the reaction between Cs and HCl, another supposedly vigorous reaction, if the Cs and the HCl are both of a quantity of 1M, the amount of H2 gas produced will be again: 1g. I thought that the reaction between Cs and HCl was supposed to be extremely dangerous but, according to the amount of H2 produced it doesn’t seem so.

So, what is wrong with my thinking? Are my calculations incorrect? Please help me because this problem is driving me insane!!

[greg1917]

The amount of heat produced is large and the reactions occur very quickly, emaning a large amount of energy is released in ashort time. In the case of Cs, its denser than water so will sink which is why you lab demonstrator usually wont show you the Cs in water reaction; it has a habbit of blowing beakers into pieces.

[VendingMenace]

first off, your calculatoins are correct. So the only thing that remains is to assess what you mean by "dangerous."

 

If by dangerous you mean by undergoing this reaction the universe will cease to exist, then no, it is not dangerous. However, if you mean, by doing this reaction could i end up with glass embedded in me, then yes, it could be dangerous.

 

What you have to look at is the following. Does the reaction release heat? If so how much? Is this heat enough to ingite the hydrogen on its own? How much energy would be released by burning hydrogen? Is this reaction being done in a confined volume? Do i have sources of ingition nearby that could accidentaly ignite the hydrogen? How hot will my reaction vessel get?

 

Stuff like that. Many reactions could be dangerous, but with proper thinking and managment, they are not. So it kinda all depends on how carefull you are and what you consider dangerous to be. Yeah.

[YT2095]

Cs is extremely electro positive, and will not only react with the HCl but will spontaniously catch fire on exposure to Air as well.

the reaction with HCl as you can imagine would therefore be several orders of magnitude greater in speed becoming not only exothermic but also doing it at explosive velocities (several thousand meters per second). in fact it would be doubtfull if you could even get them to react completely as the explosion would scatter the materials asunder. most reactions of this nature are usualy done in stages, IE/ making the Ceasium into a Hydroxide 1`st, and then slowly titrating a dilute solution of this into the HCl and alowing the water to evaporate leaving your CsCl.

[Guest sedition]

From a chemical equation, how can one then determine the severity of a reaction?

[YT2095]

a rough guide would be the amount of electrons shared between the reactants and how willing they are to give them up or take them (electro negativity). the Pauling scale for simple reactions is a good guide for ionic differences and the precentage difference in ionic character.

REDOX reactions right across the board rely heavily upon this and the octet rule. this is NOT to be confused with unstable molecular bonds however, that`s a slightly different kettle of fish

[wolfson]

To measure the "stength" so called of this reaction find the energy level using Gibbs. I will so the the equation try and apply it to so the energy (enthalpy).

 

Every chemical reaction results in a change in free energy which we can measure as:

 

DG = G products - G reactants = H products - H ractants - T(S products - S reactants) = DH - TDS

 

G

Gibb's free energy (kcal/mol)

 

DGo'

Standard free energy (kcal/mol)

 

H

heat energy (kcal/mol)

 

T

temperature (KelvinO)

 

S

entropy (kcal/mol K)

 

R

universal gas constant (1.987 cal/mol K)

 

c product, c reactant:

concentration of product, reactant (M)

 

K eq:

equilibrium constant

[wolfson]

typo top Show

[YT2095]

Wolfson, you may edit your posts using the |Edit| click on thingy at the top left of the post you want to correct (typos or whatever).

it`s in the top bar next to the "posted on: blah blah"