Quote (russian @ Jan 7 2015 04:05pm)
Single replacement means that one element will switch places with another. Make sure that a cation replaces a cation, which means that typically, a metal replaces another metal (or hydrogen).
So:
1: CuO + H2 -> H2O + Cu
2: HNO3 + Fe -> Fe(NO3)3 + H2. Presumably you can balance these on your own, it's quite easy. Just make sure the same number of each atom is on both sides. In this case, for example, you get 6HNO3 + 2Fe -> 2Fe(NO3)3 + 3H2
Double replacement is almost the exact same thing, you just don't have a free element.
3: NaOH + HCl -> NaCl + H2O
4: NaCl + H2SO4 -> NaSO4 + HCl (balance this)
Decomposition, like you said, is breaking them. But they break into free elements, so you have to respect the molecular structure. Oxygen, for example, is O2 in elemental form.
5: SO3 -> S8 + O2 (balance this)
Synthesis is combining them. Just make sure you respect their oxidation number. Al, for example, is 3, and oxygen is 2. You must have the same total oxidation number for both elements.
8: Al + O2 -> Al2O3 (balance this)
2SO3 --> 2SO2 + O2
This post was edited by RzChaos on Jan 8 2015 06:28pm