It is definitely possible to do chemistry 3/4 without 1/2 as long as you try hard and get the relevant 1/2 topics done (for instance, concepts of mole and related calculations, stoichiometry, different inter/intramolecular bonding, the list goes on). And not having lab shouldn't be a problem at VCE level. But I wouldn't suggest you to do chemistry 3/4, not because you are doing Distance Education, but since you are already doing 5 subjects and you are doing well in them, doing six 3/4 subjects in one year is too much in my opinion. Also, since you have biology already, chemistry is only needed for med and some weird courses that require 2 sciences as far as I know. However, if you really like chemistry and are willing to devote a lot of time to it, chemistry is a good and fun subject to do, but in my opinion, you should consider dropping one of you current subjects and do chemistry.