A slight problem you may encounter
Some people have a weak spot when it comes to calculations for Physics and Chemistry A-levels!
It is probably not your fault. GCSEs leave you totally unprepared for real study and the teaching in this area is terrible! I struggled too, until I took things into my own hands and went through the Calculations for A-level Chemistry and Calculations for A-level physics books. They make the whole thing quick and easy and once through you can easily handle anything the real exam throws at you. For A-level chemistry this calculation book has some incredible recommendations and sounds awesome, but I haven’t personally used it. My advice is to buy them early and use them throughout each module.