# Double Displacement Reactions that produce gas [closed]

What type of double displacement reactions can form a gas. How can i determine if a double displacement reaction will form a gas?

## closed as too broad by Philipp, Klaus-Dieter Warzecha, Michiel, user2117, tschoppiApr 3 '14 at 17:09

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• I can't give you a general answer but just looking at this wiki page you'll find at least two examples: en.wikipedia.org/wiki/Salt_metathesis_reaction – CTKlein Apr 2 '14 at 21:00
• "How can i determine if a double displacement reaction will form a gas?" I think the only thing to to is watch if one of the product is a gas... – G M Apr 2 '14 at 22:50

Reacting acids with carbonates will produce carbon dioxide gas:

$$\ce{CaCO3(s) + 2 HCl(aq) -> CaCl2(aq) + CO2(g) + H2O(l)}$$

With double replacement reactions you generally either get:

1.) A neutralization reaction

$$\ce{HCl(aq) + NaOH(aq) -> NaCl (aq) + H2O(l)}$$

2.) Gas displacement

$$\ce{CaCO3(s) + 2 HCl(aq) -> CaCl2(aq) + CO2(g) + H2O(l)}$$

3.) Precipitation

$$\ce{NaCl(aq) + AgNO3 (aq) -> NaNO3(aq) + AgCl(s)}$$

Thus it is important to know your solubility rules.

Do redox reactions count? What about a some gas other than carbon dioxide then?

Transition metal halides are reduced by $\ce{CN-}$ and form cyano complexes, while a part of the cyanide is oxidized and released as dicyan:

$\ce{2 CuCl2 + 10 KCN -> 2 K3[Cu(CN)4] + (CN)2 ^ + 4 KCl}$

$\ce{AuCl3 + 4 KCN -> K[Au(CN)2] + (CN)2 ^ + 3 KCl}$