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
Reactants and reagents are the substances that are used to bring about the chemical reaction. A reactant is any substance that is consumed or used up during the reaction. Mixtures and solutions are different from chemical reactions as the molecules of the substances stay the same. 2  Most cars get their power from an engine that uses a combustion chemical reaction. 3  Rockets are propelled by the reaction that occurs when liquid hydrogen and liquid oxygen are combined.