0am:The Winthrop, MA forecast for Mar 16 is 23 degrees and Clear. There is 70 percentage chance of rain and 21 mph winds from the West. 3am:The Winthrop, MA forecast for Mar 16 is 22 degrees and Clear. There is 73 percentage chance of rain and 19 mph winds from the West-Southwest.
Noun. 1. reactant-a chemical substance that is present at the start of a chemical reaction. chemical, chemical substance-material produced by or used in a reaction involving changes in atoms or molecules.1  Facebook.eactant. n. 1. (Chemistry) a substance that participates in a chemical reaction, esp a substance that is present at the start of the reaction. Compare product 4. (riËaek riËÃ¦k). tÉnt
Yousuf Hemani, Engineer, Volunteer, Teacher. Views. reactant: A substance participating in a chemical reaction, especially a directly reacting substance present at the initiation of the reaction. reagent: A substance used in a chemical reaction to detect, measure, examine, or produce other substances. Written May 31, 2012 Â· View Upvotes. More Answers Below.