Sulphur is often represented as S in chemical equations for several reasons:

1. Simpler Representation: In chemical equations, the focus is on the reaction and transformations between different elements and compounds. Using the symbol S instead of S8 simplifies the notation, making equations easier to read and understand.

2. Generalization of Reactions: Chemical equations aim to represent the overall transformation of reactants to products. By using S, it becomes applicable to various forms of sulphur, such as elemental sulphur (S8), sulphide ions (S2-), or other sulphur-containing species, without specifying a particular molecular form.

3. Stoichiometric Considerations: In stoichiometric calculations and balancing chemical equations, using S allows for a more generalized representation of the amount of sulphur involved in the reaction. For example, if a reaction involves 2 moles of elemental sulphur, it can be represented as 2S, rather than explicitly stating 2S8.

4. Thermodynamic and Equilibrium Studies: In thermodynamic calculations and equilibrium studies, the use of S instead of S8 simplifies the analysis and mathematical treatment. It allows for the consideration of various sulphur species and their contributions without delving into specific molecular structures.

5. Common Practice: The convention of using S to represent sulphur in chemical equations is widely accepted in the scientific community and has been consistently employed in textbooks, scientific literature, and research papers for many years.