Here is a comprehensive summary of Units 15-25 of OCR A Level Chemistry, covering advanced topics essential for exam success: 15. Unit 15 - Chemical Equilibria: Focuses on dynamic equilibrium in chemical reactions, Le Chatelier's Principle, and equilibrium constants (Kc and Kp). The unit explains how changes in temperature, pressure, and concentration affect equilibrium positions and how these concepts are applied in industry. 16. Unit 16 - Transition Elements: Explores the chemistry of t...