[Electro057]

CuCl3+Mg

Because we saw the Mg gave off bubbles and it appeared as if the Mg was eroding.  Also rust was forming at the bottom my lab partner said it ws decomp.

I say that because the reactants are in the form AB+C it is single displacement which should result in CB+A

what kind of reaction is this?  My lab partner thinks it's decomp but i think it's single displacement. we can't hand in different labs!

[Yggdrasil]

It's a single replacement reaction.  It's definitely not a decomposition because rusting isn't a decomposition in the first place.

[wereworm73]

Your "rust" might have been copper residue.  If you really used a copper(III) compound, I think the reaction would be this:

2CuCl₃ + 3Mg ---> 2Cu + 3MgCl₂

[xiankai]

if its decomposition, then where does the Cl go? ask your lab partner that.