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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: pzona69 on January 07, 2008, 03:22:29 PM

Title: Alkali Metals + Water
Post by: pzona69 on January 07, 2008, 03:22:29 PM
I know that when alkali metals react with water, things usually get pretty violent, but I was wondering what the equation looks like. My guess would be Na (as an example) + H2O -> NaOH + H2.

I was just thinking about this, as someone mentioned metallic sodium in another topic, and I wondered what type of reaction takes place in water.
Title: Re: Alkali Metals + Water
Post by: Kryolith on January 07, 2008, 03:24:05 PM
Your equation is almost right, just try to correct the stoichiometry. Do you know what kind of reaction is it?
Title: Re: Alkali Metals + Water
Post by: pzona69 on January 07, 2008, 10:54:53 PM
Ah, I forgot:

2Na + 2H2O -> 2NaOH + H2

Single replacement reaction if I'm not mistaken? I was also going to ask what makes the alkali metals so reactive. I was thinking it's just the common oxidation state of +1?
Title: Re: Alkali Metals + Water
Post by: Arkcon on January 07, 2008, 11:17:02 PM
Quote from: pzona69 on January 07, 2008, 10:54:53 PM
I was also going to ask what makes the alkali metals so reactive. I was thinking it's just the common oxidation state of +1?

Yes, the alkali metals are all +1.  But there is a continuum of electronegativities, based, for the most part on atomic radius. see {wikipedia} (http://en.wikipedia.org/wiki/Electronegativity#Electronegativities_of_the_elements)
Title: Re: Alkali Metals + Water
Post by: Kryolith on January 08, 2008, 04:30:37 AM
Quote from: pzona69 on January 07, 2008, 10:54:53 PM
Ah, I forgot:

2Na + 2H2O -> 2NaOH + H2

Single replacement reaction if I'm not mistaken? I was also going to ask what makes the alkali metals so reactive. I was thinking it's just the common oxidation state of +1?

Your equation is correct. I just googled for "single replacement reaction" and I guess your answer is ok. I would have called it an redox equation. Alkali metals have very low ionization energies, so they are very reactive.

Title: Re: Alkali Metals + Water
Post by: pzona69 on January 08, 2008, 03:11:39 PM
Well yeah, I knew it was a redox equation, but I was trying to say more than that the oxidation state just changed. 

Also, I don't really understand what you mean about the ionization energy. Ionization energy is directly proportional to electronegativity (from what I understand anyway), and the halogens, which generally have high electronegativity, are also very reactive.
Title: Re: Alkali Metals + Water
Post by: Kryolith on January 08, 2008, 03:28:10 PM
Quote from: pzona69 on January 08, 2008, 03:11:39 PM
Well yeah, I knew it was a redox equation, but I was trying to say more than that the oxidation state just changed. 

Also, I don't really understand what you mean about the ionization energy. Ionization energy is directly proportional to electronegativity (from what I understand anyway), and the halogens, which generally have high electronegativity, are also very reactive.

Ionization energies are calculated/determined for free atoms, EN for chemical bonds.
The halogens are indeed reactive (trend within the main group?). But how do they react, in comparison to alkali metals? Is the ionization energy relevant?