Course Introduction This course covers the Air section of Topic C1: Air and Water which are examined in Papers 2 and 4 of  the GCSE OCR Combined Science B Course. This course aims to answer several questions including: C1.1 How has the Earth’s atmosphere changed over time, and why? C1.2 Why are there temperature changes in chemical reactions? C1.3 What is the evidence for climate change, why is it occurring? This Topic is completed by Potable Water: GCSE OCR Combined Science B. The following information, included in this course, is assessed at Higher Tier only: The limitations of the particle model in relation to changes of state when particles are represented by inelastic spheres Calculations of energy changes in a chemical reaction by considering bond breaking and bond making energies