Its true it really comes down to the interview but I really don't know anyone having gotten in with a 97 atar. I'm assuming with that kind of atar you'd need an incredibly high umat and a good interview.
For UNSW: median is around 99.6 atar and around 96 umat although you can get in with your atar as long as you have a high 90's umat and an interview i would say roughly in the top 1/4 of interviewees
For UWS: median of about 95 umat as well? atar doesn't count once you pass the threshold atar of...
Some basic knowledge of chemistry will definitely be useful, however it is pretty fundamental content you can definitely learn by yourself after HSC. Really all you need to know are basic concepts taught in year 11 chemistry such as for example different types of bonds such as covalent and ionic...