If it is a simple single-molecule first-order reaction, the rate is doubled.

If it is a simple second-order reaction in which the same molecule collides, the rate becomes 2*2=4 times.

If it is two reactants, A+B, and it is the second-order reaction of A-B bimolecular collision, then see how many times the concentration of AB becomes, and multiply the two times to get a new multiple.

And so on, multiple mechanisms, multiple algorithms.