So, I actually taught first year at Chemistry for quite a few years, and Sine has basically hit the nail straight on the head, but here's some facts that I think are super relevant:
1. In some years, more than 30% of students enrolled in CHM1011 and CHM1022 (the first year chemistry university subjects) did not do high school chemistry.
2. The distribution of scores of students who did not do high school chemistry was not significantly different to the distribution of scores for students who DID do high school chemistry - in simpler language, doing VCE chemistry did not mean you were more likely to get a good score.
Now, there are some things to consider - those who did do VCE chemistry definitely had less studying or reading in some topics because it was very similar to what they did in high school, or had background knowledge that made some things easier. But, Monash is very good at starting from scratch and really building your knowledge up where you should be fine even if you don't have high school chemistry knowledge or skills.
But even more importantly - that's only if you choose to study first-year chemistry at all! I will say, if you have any interest in human or medical biology, first year chemistry is a very useful sequence to have (particularly if you go on to do biochemistry). But, it's up to you if you include it, and not doing first year chemistry will only lock you out of majoring in chemistry. If you don't think you'll do first year chemistry, then it really doesn't matter if you do VCE chem or not. If you think you might maybe want to, then know that Monash has designed the course such that whether or not you did VCE chem doesn't really impact how well you do in the subject, anyway.