HELP! I don't understand how to know what the formula of the product will be just by knowing the reactants...!

Question

Any reactants.
Isn't there a general rule?

I know about the criss-cross rule but that only works when there are 2 reactants.

Answer 1

the formula of the product will simply be the same elemental composition as the reactants, only rearranged in a different form. Whatever is on one side must be in equal proportions on the other. of course, a concrete example would be nice.

N2 + O2 ----> 2NO

not too bad.

Answer 2

there are only a few normal kinds of reactions possible. if you have 2 separate reactants, the products will be those two reactants joined.

such as:
Na+Cl --> NaCl

if the reactant is one compound, the product will be those two separated.

such as:
NaCl --> Na + Cl

if the reactants are a compound and an ion or atom, the two with the same type of ionic (meaning positive or negative) charge will switch places.

such as:
NaCl + K --> KCl + Na

If the reactants are 2 compounds, the ones with the same type of ionic charge will switch places.

such as:
NaCl + KOH --> NaOH + KCl
(in this case, the other one taking the place of Cl is OH, which is hydroxide ion, made of hydrogen and oxygen, which has a charge of 1-)


In all the examples shown, the charges were all 1- or 1+, which made it very easy to add together. Sometimes, the charges will not be the same, so you must put the correct number of each reactant and product atom so each molecule has a balanced charge (meaning it evens out to 0). In addition, you must have the same number of each atom on each side.