In a chemical equation, what are the substances on the left side called?

• A. Reactants
• B. Products
• C. Catalysts
• D. Solvents

Answer: (A)

The left side of a chemical equation lists the starting materials that participate in the reaction, and these are called reactants. They undergo chemical change to form new substances on the right side, which are the products. The arrow or yields sign separates what you start with from what you end up with, and balancing the equation ensures the same number of atoms of each element on both sides. The coefficients in front of the substances indicate how many molecules or moles participate. Catalysts may appear in a reaction to speed it up without being consumed, so they can show up in the equation but aren’t the focus when naming the left side as reactants. Solvents are the medium for the reaction and aren’t listed as reactants unless they actually participate in the reaction. For example, in H2 + O2 -> H2O, H2 and O2 are reactants on the left, and H2O is the product on the right.