You first need to have a Bachelor's degree in any field/profession, before you can opt for Masters or PhD.
I don't really think a bachelor's degree in "Computer Engineering/Computer science/IT" might get you eligibility for a PhD in both Physics and chemistry.
Okay, this might also depend on the University/college, but these are 2 different fields, if I'm not mistaken. First get a bach degree in Physics and Chemistry, so that you can apply for a masters/PhD later on.