Some general questions

[EIRE2003]

Why do some substances react with other while others do not?

How fast does a chemical reaction occur?

[chem_tr]

This is a very general question :smile:

Well, some react with others since they are in the same phase; some of them don't, because they are in solid form while the other is liquid therefore they cannot combine. In such cases, we only expect that the reaction occurs at the interfaces.

About reaction rates, since it is in a molecular basis, it is unpredictably fast; but Ahmed Zewail has managed to catch "molecules" via femtochemistry. You can understand that the rates are as fast as 10-15 s.

[Sirus]

How fast does a chemical reaction occur?

There is a whole section of chemistry called reaction rates. Reaction rates are entirely specific to each reation. They depend on a number of things, among others temperature, concentration of reactants, nature of the reactants, and presence or absence of a catalyst.