As a full time chemistry tutor, I have seen many students spending 5-10 hours a day studying without learning well. I tell many of my students that studying is not about how many hours you spend but rather how effectively you do it.
3 Ways to make your studying more productive:
1. Use different resources. Use a combination of textbook, youtube videos, and google. When you learn material from different resources, you are able to understand this material broadly and in different scenarios.
2. Practice, practice, practice
For a science class such as chemistry, physics, and biochemistry practice is essential. Yes, you can read the book and understand the theory but the only way you can learn how to apply that theory is through a lot of practice. Practicing from different sources will also make you able to solve problems from the same topic presented in various ways.
3.Start to study early and consistent.
Don't wait until last minute. There is no need to pull all nighters. All you need to do is start early and keep on practicing every day. If you do, you will not have to cram right before the exam.