The First Law of Thermodynamics, also known as the Law of Energy Conservation, states that energy cannot be created or destroyed, only transformed from one form to another. In the context of reacting systems, this principle plays a critical role in understanding how energy flows and changes during chemical reactions. In any chemical reaction, whether it is exothermic (releasing energy) or endothermic (absorbing energy), the total energy of the system must remain constant. The energy involved in the reaction is typically in the form of heat and work, and both are linked to the internal energy of the system. Internal energy includes the energy associated with the bonds between atoms and molecules, the kinetic energy of molecules, and the potential energy stored in the system due to interactions between particles. For a reacting system, the First Law can be mathematically expressed as: [ \Delta U = Q - W ] Where ( \Delta U ) is the change in the internal energy of the