Reaction type is pretty straight forward, there are key things to look for.
Anything dealing with propane or a gas will most likely be a combustion reaction. Another way to know is that a combustion reaction will result in the production of C20 and H2O.
Decompositon is when you have a compound produces two more substances.
Oka, Here's a simple way to remember:
Formation(synthesis/composition)
E + E --> C
Element + element --> compound
i.e.. 2Na + Cl2 --> 2NaCl
So you'll have a product which is a combination of the two reactants.
Decomposition Reaction
C --> E + E
Pretty much a reverse of the above.
i.e.. 2HgO --> 2Hg + O2
Combustion (think of 'burn')
Hydrocarbon + O2(g) --> CO2(g) + H2O(g)
The O2(g) --> CO2(g) + H2O(g) will always remain the same, never change, in these reactions.
Single and Double Replacement are really simple and straight forward.
Single Replacement
E + C --> new E + new C
So i.e..
Cu(s) + ZnO(s) --> CuO(s) + Zn(s)
You swap the Cu and the Zn, you do this because they are both 'positive'
Double Replacement
C + C --> newC + newC
i.e.. NaCl(s) + KBr(s) --> NaBr + KCl
You can swap either the positives or the negatives that are before the arrow.
In this case the two positives are swapped again. Na and K to form the two new compounds.
So when you look at a question, write out what you know, figure out what you need to know and what needs to be formed.
Na2CO3(aq) + HCl(aq) --> NaCl(aq) + CO2(g) + H2O(l)
Aqueous sodium carbonate + aqueous hydrochloric acid --> sodium chloride + carbon dioxide + water
You have compound+compound --> compound + element + element
Think about it...
Once you learn the types of reactions everything will come easier.
Like you asked what about
Zn + H2CO3 -->
You have an element + compound
So you're going to have a single replacement reaction occurring, right?
You need a new element and a new compound to be formed.
Think you can figure it out?
I know this isn't much help but I hope it gave you a start. If you're confused about anything let me know.
This is a great site to help you out, so check it out if in doubt okay.
http://www.chemtutor.com/react.htm
Good luck.