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
Photos.com/AbleStock.com/Getty Images. A chemical reaction is the transformation of one or more chemical substances, called reactants, into another set of chemical substances, called products.. Chemical reactions involve the breakage and formation of chemical bonds, and this has an associated transfer of energy.ndothermic Reactions. Endothermic chemical reactions absorb energy from their surroundings. Usually these reactions cause the surroundings and the reaction mixture to decrease in temperature.