Molecular Weight of Reactants in Chemistry Formulas

Yes, the Molecular Weight of Reactants, measured in Molar Mass can be negative.

Molecular Weight of Reactants is usually measured using the Kilogram Per Mole[kg/mol] for Molar Mass. Chlorine Molecule (Cl2) Molecular Mass[kg/mol], Gram Per Mole[kg/mol], Hydrogen (H) - Standard Atomic Weight[kg/mol] are the few other units in which Molecular Weight of Reactants can be measured.