If someone could quickly tell me whether the reaction between Calcium Carbonate + HCL which forms Calcium chloride + water + calcium dioxide is a double displacement reaction, or an acid-base (neutralisation) reaction. It would be really appreciated.
Be careful with the phrase "double displacement", there are disputes about what it actually means.
Any reaction in which there is a clear swapping, as in
AB + XY ---> AY + BX
can be called double displacement, but there are cases that I would not call a double displacement.
For example. consider putting silver(I) nitrate solution into sodium chloride solution:
AgNO
3(aq) + NaCl(aq) ---> AgCl(s) + NaNO
3(aq)
Certainly looks like double displacement, but if we look at it in net ionic terms, we have:
Ag
+(aq) + Cl
- ---> AgCl(s)
which is clearly a precipitation and arguably a combination. The sodium and nitrate ions were floating about in the two solutions on their own before the solutions were mixed and are still there once mixing has occurred. They are spectators, taking no part, and the notion that sodium nitrate has formed is misleading.
Notions of single displacement and double displacement are popular in US chemistry texts but much less common in Australia, and the use of them in the US is both inconsistent and (at times) confused. It arises from trying to apply a classification system to chemical reactions that is based on superficial similarities rather than grouping them by chemical nature. I would definitely advise thinking of this as an acid/base reaction or a type of neutralisation, reflecting the chemical behaviour within the system.
