Law school admissions won’t care even the tiniest bit what you study in college.
For Chem & PoliSci that is generally not an issue: in most universities they are in the same school (“Arts & Sciences” or similar). The gift of the US system is that this is not a decision you have to make for at least a couple of years. If you have any preference at all for one or the other, name that as your proposed major- it just means that your first advisor will be from that department and if there are course selections that fill up fast you will be 2nd from the bottom instead of at the bottom of the hierarchy list as to who gets the places.
Sign up for the intro classes to both majors and see what you like. Everybody here will have anecdotes, but some examples from the kids in my bailiwick include a planned IR major who discovered she loathed IR theory but loved cellular biology, a planned Chem major who ended up a Philosophy & Math double major, and so on.
Also, the whole major/minor/double major thing turns out to matter very very little (if at all): you might be happiest majoring in X, and taking a lot of electives in Y, but not making it a formal major or minor.