Well first of all it depends whether you like the subject and you find it interesting because some of the topics can be slightly boring. If you're good at the subject and you like it then you automatically will show some determination to get a high grade. But overall I find chemistry quite easy, some of the organic chemistry can be hard but as long as you expose yourself to a lot of exam questions and you know the basics then chemistry is not hard at all!
yes, but not too much if you're into core chemistry with a lot of equations and less on how science works. It is the most respected out of the three sciences at A-Level as it considered the hardest. but work hard and I'm sure you'll reap the benefits.
It is quite demanding but ive heard that Physics is solid! So its not all that bad but I suggest you begin revision early...itll make your workload a whole lot lighter and you wont have to do many late nights which can be very exhausting and draining!!