USC engineering accepts IB chemistry HL score of 6 for CHEM 105a, according to http://viterbinotes.usc.edu/wp-content/uploads/2014/04/AP-IB-Sheet-2014.pdf (if you are in another division, check with the division or major to see if that applies to your intended major).
Otherwise, if you want to take CHEM 105a, you have to take a placement test covering high school chemistry: https://sait.usc.edu/academicsupport/cta/placement_chem.shtml