In science, reaction (TR:625) (LH:28) (TL:653|#48), from Latin reagere “react”, from re- “back” + agree “to do, act”, is one action equal and opposed to another action, with respect to the mutual actions of two bodies upon each other, being equal and directed to contrary parts, according to the third law of motion (Newton, 1687); a process in which there is a change in bonds, wherein reactants transform into products (Cullen, 1757).
The following are related quotes:
- “To every ‘action’ there is always opposed an equal ‘reaction’: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.”
- — Isaac Newton (1687), Principia 
- Reaction – Hmolpedia 2020.