The Primer describes the basic principles which govern reactivity and phase equilibria in chemical systems. It is written at the first year undergraduate level and contains a number of worked examples and problems to help students through this introductory material. The ideas of enthalpy, internal energy and entropy are covered to lead into Gibbs free energy and how it can be used to correlate and predict the equilibrium position and properties of chemical reactions and multi-phase systems. Some background mathematical ideas are introduced as needed as well as material describing how the physicochemical principles can be applied to related areas such as materials science or biochemistry.