Gas evolution question

[tennisboy85]

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Hi,
This question has been bothering me for a while, and I think it might have been asked in the past, but I couldn't find the thread. Anyhoo, I was wondering in what situations would H2, C02, or other gases be formed? Is there a general rule to follow?

For example, I think most metals in water produce H2, but I don't know the specific rule for it.

Also, on one of the AAMC, Cu in HN03 somehow produces N0, which never really made much sense to me either.

If someone could help out with this, that'd be great.

 

[jhh3000]

typically an alkaline metal in water will evolve hydrogen gas because water is comprised of H and O atoms, and metals reduce hydrogen, not oxidize oxygen. as a general rule if HCO3 is in the reactant mixture, CO2 will evolve, and if HNO3 is, NO will evolve. it also has to do with what's most easily reduced by the metals (remember that metals, especially alkaline metals, have extra electrons and thus like to give them away. which is why they react so violently with water)

 

[ChePibe]

The above poster is right. Remember that alkali metals (group I) react violently with water to evolve gases. Furthermore, remember the oxidation reduction capacities of the compounds involved in the reaction. Transition metals are always oxidized (lose electrons) in these reactions. Keeping this in mind it means that the other compound will be reduced. Also keep in mind that transition metals want will first loose the e- from the s orbital first and that they will want to reach a stable final configuration (having the d orbital either fully filled or half filled). The case of the Cu, I'm not too sure, but itseems as though the Cu is reacting with the HNO3 to form CuNO2 and NO gas. I'm sure the passage in this case should give you some insight into what is going on this case.
Hope this helps some.

PD: Did you watch the Djokovic-Federer match yesterday? It was a great match!

 

[axp107]

These questions still confuse me =(

HCO3 in water.. hmm

HCO3 + H2O .. why would CO2 evolve in the first place.. and how do you know its CO2 and not CO

I wish there were some quick and dirty rules to figure out rxns like this

 

[DrknoSDN]

Digging up old thread.

I missed a question related to gas evolution from a chemical reaction. Does anyone know of any other gas evolution reactions other than these: And if they are incorrect please correct me. Thanks.
Zinc + HCl > Hydrogen gas
H2CO3 -> CO2(g) + H2o
H2SO3 -> SO2(g) + H2o
NH4OH -> NH3(g) + H2O
HNO3 -> NO2 + O2 + H2O (red vapor)
HNO3 + H2O -> NO(g)

Any additional study notes appreciated. Under what conditions do mono substituted gases (Carbon monoxide etc) evolve as the major product? Thanks again.

 

[whistle47]

this was helpful

http://chemistry.stackexchange.com/...es-hno3-not-give-off-h2-when-reacting-with-cu

posting for future google search arrivals