I've never done Chemistry, but I'm more than happy to give you some advice on Extension History!
If you are thinking of a science-based course/career after school, then I'd recommend you keep chemistry because it's recommended for a lot of courses in that area.
However, Extension History was my absolute favourite class this year, and I cannot recommend it enough. Usually the classes are fairly small because it's not the most popular subject out there, so the atmosphere is usually a bit more relaxed.
I found that it really helped me a lot with Modern History. The standard expected for the essay writing in Extension is quite high, and throughout the course you'll find that your writing will become a bit more sophisticated and cohesive. You will be doing A LOT of essay writing in Extension. I also found it to be really useful for the source analysis in WW1. I don't do Ancient, but all three of my extension classmates did and they also found it to be really useful. All the historiography that you do in Extension can really give you an edge over your classmates in 2 unit.
While the workload is a little more than you'd expect for a 1 unit subject, it is not as bad as it seems. The project can really eat into your time though, as it makes up 80% of your internal mark. If you choose the right topic for your project, then you'll enjoy working on it and it won't seem like such a chore. You need to put in a consistent effort for the written exam though, so you'll need to spend roughly two or so hours a week during non-exam periods.
The project was my favourite part of the course, and I cannot stress enough how important it is to choose something that interests you. Don't just choose a topic because you think it will get you into the top-band. Choose something that you love, something that really fascinates you. This is also an excellent opportunity to study something that you wouldn't normally be able to in 2 unit, eg an Ancient student doing a Modern topic for their project and vice versa, or even something that isn't covered in either the Ancient or Modern syllabus, such as medieval history or early modern.
The first section of the written component (Historiography), in my opinion, is really quite boring, however it is fairly easy to master for the exam. The exam situation for this question isn't any better, they can throw anything at you. They also usually give you a really long source that you have to incorporate into your answer. The case study for me was much more interesting, we did JFK and I absolutely loved it.
Extension history is a completely different subject to Chemistry. Obviously the subject matter is different, but the requirements of each course are quite different too. Extension doesn't have a structured syllabus like chemistry does, so you can't really predict any areas of the exam. You can't really write your notes by the syllabus dot points because in Extension, there are no dot points, so you're on your own when it comes to note-taking. Also, be prepared for lots and lots of reading in Extension.
If they allow it at your school, why don't you trial Extension history for a term or so, and then make an informed decision in Term 1 next year?
