In a general sense, how do you determine what the product will be in a chemical reaction? In the first example, a gas evolution, you combine the cation of each compound and pair it with the anion of the other:
HNO3(aq) + Na2CO3(aq) ----> H2CO3(aq) + NaNO3(aq)
However, in other examples, its less intuitive. I understand what synthesis, decomposition and displacement reactions are, more or less...But I still cant figure out why the results are the way they are. For instance, the next example shows:
CaO(s) + CO2(g) ----> CaCO3(s)
Here it shows a synthesis reaction, rather than the cation and anion mix and match (Double displacement). And the last example shows a similar one to the CaCO example:
SO3 + H2O ----> SO + H2O3
In this example, they did use double displacement rather than what they used for the CaCO reaction.
Why is that? And how does one determine what the result will be by looking at the reactants?
Synthesis ---> A+B = AB
Decomposition ---> AB = A+B
Displacement ---> A+BC = AC+B
Double displacement ---> AB+CD = AD+CB