A Chemical Reaction Is a Process That Leads to the Chemical Transformation of One Set of Chemical Substances to Another. Classically, Chemical Reactions Encompass Changes That Only Involve the Positions of Electrons In the Forming and Breaking of Chemical Bonds Between Atoms, With No Change to the Nuclei (No Change to the Elements Present), and Can Often Be Described By a Chemical Equation. Nuclear Chemistry Is a Sub-Discipline of Chemistry That Involves the Chemical Reactions of Unstable and Radioactive Elements Where Both Electronic and Nuclear Changes Can Occur.
The Substance (Or Substances) Initially Involved In a Chemical Reaction Are Called Reactants or Reagents. Chemical Reactions Are Usually Characterized By a Chemical Change, and They Yield One or More Products, Which Usually Have Properties Different from the Reactants.