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
1 A physical change, such as a state change or dissolving, does not create a new substance, but a chemical change does. 2  In a chemical reaction, the atoms and molecules that interact with each other are called reactants. 3  In a chemical reaction, the atoms and molecules produced by the reaction are called products.xplain that in most chemical reactions, two or more substances, called reactants, interact to create different substances called products. Tell students that burning a candle is an example of a chemical reaction.