The syllabus for all the sciences are quite long i admit but all the stuff are linked and connected. you learn one thing and its networked in relevance to alot of other things. that is a science. so imo chem isnt hard at all, it is worth it. so is physics. in fact, physics is prolly the easiest 2u subject i cud think of (besides 2u maths) cos its just common sense! i mean pfft if ur inquisitive and stuff u wudve gathered a library of knowledge of everyday phenomena and why they occur simply by observation / asking ur parents etc. physics is basically expanding upon this, and giving obvious stuff jargon names. its so friggin worth it.
imo eng ext1 by itself is totally not worth it. ur expected to be a 'books' person, i.e. they give u a 4cm thick novel to read in one week on a regular basis.