Chemistry_Keegan
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Neutralization Reaction Question
I have been asking myself this question for a long time, and this seems like a good place to get it answered. You know how allot of acids and bases
aren't liquid at room temperature? Well what if instead of dissolving them, we changed their temperature or pressure to make them liquid? An example
for an acid would be if we were to cool hydrogen chloride to the point it became liquid, instead of dissolving it in water to make hydrochloric acid.
An example for a base would be if we were to melt sodium hydroxide. Would these compounds still react like regular acids and bases (perform a
neutralization reaction), or would something weird happen?
[Edited on 18-2-2013 by Chemistry_Keegan]
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kristofvagyok
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You are right, something weird: it would blow in your face.
HCl is liquid under -85 Celsius and NaOH melts at +320 Celsius. Just the simple difference between these two temperatures and the fact that one one
the reactants is a gas could easily cause problem. And if we also add the highly exothermic acid-base reaction between them...
I have melt NaOH just a few times ever. At first we've needed to make abs. pyridine what is produced by pouring waterfree, molten NaOH from a silver
crucible in a large breaker what contained pyridine under argon. It wasn't as funny as it sounds.
A girl made it and at the first attempt she accidentally poured a little molten NaOH next to the pyridine, right on the table and the floor. The wood
table still today looks like it have suffered from a meteor shower. Imagine this by pouring it on liquefied HCl.... Disaster on the
horizon.
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Chemistry_Keegan
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Wow, that's a pretty cool story you have there. 
But what if there wasn't a huge temperature difference? Like solids with lower melting points and gases with higher condensation points?
[Edited on 18-2-2013 by Chemistry_Keegan]
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elementcollector1
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It would likely still blow in your face, as the acid/base reaction is well-known for being violent.
Elements Collected:52/87
Latest Acquired: Cl
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blogfast25
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Nope. The reaction enthalpy of a neutralisation reaction is 57 kJ/mol, that’s not really a lot. In reality even fairly concentrated acid and alkali
solutions can be combined safely if a few calculations are made in advance and the liquids are combined slowly with intense stirring. I do this all
the time. Above certain concentrations there’s the risk that the formed salt is forced out of solution (solubility limit) and then the lattice
energy released can cause sudden bursts of boiling and steam release.
The reaction in question that Keegan is referring to is better not referred to as an ‘acid base neutralisation’.
Acids and bases in the Bronsted-Lowry sense of the word are relative to a protonatable solvent, usually (but not exclusively) water.
When HCl dissolves in water it reacts with it:
HCl(aq) + H2O === > H3O+(aq) + Cl-(aq) (protonation of water)
The oxonium ion (H3O+) is what gives acid solutions their acid taste.
Sodium hydroxide dissolves in water by dissociating:
NaOH(s) === > Na+(aq) + OH-(aq) and the hydroxide ion (OH-) gives such solutions their soapy taste.
When the solutions are combined the Na+ and Cl- ions don’t actually do anything, only the oxonium and hydroxide ions combine to form water:
H3O+(aq) + OH-(aq) === > 2 H2O(l)
This generates heat, known as the Enthalpy of Neutralisation (about 57 kJ/mol), which is why neutralising causes the solution to heat up.
But by combining pure, liquid HCl and molten NaOH, not only water would be produced but also solid NaCl and that would generate enormous amounts of
heat.
[Edited on 18-2-2013 by blogfast25]
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